chore(lint): Fix suppressed ESLint errors in remote-feature-flag-controller package (#7428)

## Explanation

This fixes all suppressed ESLint errors in the
`remote-feature-flag-controller` package.

## References

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* Fixes #12345
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Closes #7388.

## Checklist

- [ ] I've updated the test suite for new or updated code as appropriate
- [ ] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [ ] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/contributing.md#updating-changelogs)
- [ ] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Adds explicit types and a private method refactor to the client config
service, tightens test typings/utilities, and removes related ESLint
suppressions.
> 
> - **Remote Feature Flag Controller**:
>   - **ClientConfigApiService (`client-config-api-service.ts`)**:
> - Add explicit return types for `onBreak`/`onDegraded`
(`IDisposable`).
> - Refactor `flattenFeatureFlags` to private field method
`#flattenFeatureFlags` and update call site.
>   - **Controller (`remote-feature-flag-controller.ts`)**:
>     - Add explicit `Promise<void>` return type to `#updateCache`.
> - **Tests**:
> - **ClientConfigApiService test**: Import `jest.Mock`, type
`createMockFetch` to return `Mock`, adjust Promise params to satisfy
lint.
> - **RemoteFeatureFlagController test**: Annotate `createController`
return type; type `getMetaMetricsId` default.
> - **Tooling**:
> - Remove corresponding entries for this package from
`eslint-suppressions.json`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
9821288. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: Mrtenz

eslint-suppressions.json

@@ -3067,32 +3067,6 @@
       "count": 1
     }
   },
-  "packages/remote-feature-flag-controller/src/client-config-api-service/client-config-api-service.test.ts": {
-    "@typescript-eslint/explicit-function-return-type": {
-      "count": 1
-    },
-    "promise/param-names": {
-      "count": 1
-    }
-  },
-  "packages/remote-feature-flag-controller/src/client-config-api-service/client-config-api-service.ts": {
-    "@typescript-eslint/explicit-function-return-type": {
-      "count": 2
-    },
-    "no-restricted-syntax": {
-      "count": 1
-    }
-  },
-  "packages/remote-feature-flag-controller/src/remote-feature-flag-controller.test.ts": {
-    "@typescript-eslint/explicit-function-return-type": {
-      "count": 2
-    }
-  },
-  "packages/remote-feature-flag-controller/src/remote-feature-flag-controller.ts": {
-    "@typescript-eslint/explicit-function-return-type": {
-      "count": 1
-    }
-  },
   "packages/seedless-onboarding-controller/jest.environment.js": {
     "n/no-unsupported-features/node-builtins": {
       "count": 1

packages/remote-feature-flag-controller/src/client-config-api-service/client-config-api-service.test.ts

@@ -10,6 +10,8 @@ import {
   EnvironmentType,
 } from '../remote-feature-flag-controller-types';
 
+import Mock = jest.Mock;
+
 const mockServerFeatureFlagsResponse: ApiDataResponse = [
   { feature1: false },
   { feature2: { chrome: '<109' } },
@@ -265,13 +267,15 @@ function createMockFetch({
   response?: Partial<Response>;
   error?: Error;
   delay?: number;
-}) {
+}): Mock {
   if (error) {
     return jest
       .fn()
       .mockImplementation(
         () =>
-          new Promise((_, reject) => setTimeout(() => reject(error), delay)),
+          new Promise((_resolve, reject) =>
+            setTimeout(() => reject(error), delay),
+          ),
       );
   }
 

packages/remote-feature-flag-controller/src/client-config-api-service/client-config-api-service.ts

@@ -5,6 +5,7 @@ import {
   DEFAULT_MAX_RETRIES,
 } from '@metamask/controller-utils';
 import type { ServicePolicy } from '@metamask/controller-utils';
+import type { IDisposable } from 'cockatiel';
 
 import type { AbstractClientConfigApiService } from './abstract-client-config-api-service';
 import { BASE_URL } from '../constants';
@@ -154,7 +155,7 @@ export class ClientConfigApiService implements AbstractClientConfigApiService {
    * takes.
    * @returns What {@link ServicePolicy.onBreak} returns.
    */
-  onBreak(...args: Parameters<ServicePolicy['onBreak']>) {
+  onBreak(...args: Parameters<ServicePolicy['onBreak']>): IDisposable {
     return this.#policy.onBreak(...args);
   }
 
@@ -165,7 +166,7 @@ export class ClientConfigApiService implements AbstractClientConfigApiService {
    * takes.
    * @returns What {@link ServicePolicy.onDegraded} returns.
    */
-  onDegraded(...args: Parameters<ServicePolicy['onDegraded']>) {
+  onDegraded(...args: Parameters<ServicePolicy['onDegraded']>): IDisposable {
     return this.#policy.onDegraded(...args);
   }
 
@@ -194,7 +195,7 @@ export class ClientConfigApiService implements AbstractClientConfigApiService {
       throw new Error('Feature flags api did not return an array');
     }
 
-    const remoteFeatureFlags = this.flattenFeatureFlags(data);
+    const remoteFeatureFlags = this.#flattenFeatureFlags(data);
 
     return {
       remoteFeatureFlags,
@@ -211,7 +212,7 @@ export class ClientConfigApiService implements AbstractClientConfigApiService {
    * // Input: [{ flag1: true }, { flag2: [] }]
    * // Output: { flag1: true, flag2: [] }
    */
-  private flattenFeatureFlags(responseData: ApiDataResponse): FeatureFlags {
+  #flattenFeatureFlags(responseData: ApiDataResponse): FeatureFlags {
     return responseData.reduce((acc, curr) => {
       return { ...acc, ...curr };
     }, {});

packages/remote-feature-flag-controller/src/remote-feature-flag-controller.test.ts

@@ -67,14 +67,16 @@ function createController(
     getMetaMetricsId: () => string;
     clientVersion: string;
   }> = {},
-) {
+): RemoteFeatureFlagController {
   return new RemoteFeatureFlagController({
     messenger: getMessenger(),
     state: options.state,
     clientConfigApiService:
       options.clientConfigApiService ?? buildClientConfigApiService(),
     disabled: options.disabled,
-    getMetaMetricsId: options.getMetaMetricsId ?? (() => MOCK_METRICS_ID),
+    getMetaMetricsId:
+      options.getMetaMetricsId ??
+      ((): typeof MOCK_METRICS_ID => MOCK_METRICS_ID),
     clientVersion: options.clientVersion ?? MOCK_BASE_VERSION,
   });
 }

packages/remote-feature-flag-controller/src/remote-feature-flag-controller.ts

@@ -212,7 +212,7 @@ export class RemoteFeatureFlagController extends BaseController<
    *
    * @param remoteFeatureFlags - The new feature flags to cache.
    */
-  async #updateCache(remoteFeatureFlags: FeatureFlags) {
+  async #updateCache(remoteFeatureFlags: FeatureFlags): Promise<void> {
     const processedRemoteFeatureFlags =
       await this.#processRemoteFeatureFlags(remoteFeatureFlags);
     this.update(() => {