Add GetTokenOptions

[chlowell]

Closes #2566

[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

azure_core
azure_identity

[Copilot]

Pull Request Overview

This PR extends the TokenCredential API to accept an optional GetTokenOptions parameter and updates all existing credentials, cache logic, and examples to propagate it (using None by default). It also refactors the token cache to pass options through to the fetch callback.

• Extend TokenCredential::get_token to accept Option<GetTokenOptions> and add the GetTokenOptions type.
• Update every credential implementation (and calling sites) to accept and forward the new options parameter.
• Refactor TokenCache to accept and pass options to the provided callback function.

Reviewed Changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 2 comments.

File	Description
sdk/core/azure_core/src/credentials.rs	Added GetTokenOptions and updated trait signature
sdk/identity/azure_identity/src/credentials/cache.rs	Refactored cache to accept options and callback
sdk/identity/azure_identity/src/credentials/imds_managed_identity_credentials.rs	Updated get_token signature and calls

Comments suppressed due to low confidence (1)

sdk/identity/azure_identity/src/credentials/cache.rs:30

• [nitpick] No tests currently pass a non-None GetTokenOptions through the cache. Consider adding a test case that supplies a real GetTokenOptions to ensure it is correctly propagated to the callback.

pub(crate) async fn get_token<'a, C, F>(

[Copilot]

[nitpick] Consider renaming the callback parameter to a more descriptive name, such as fetch_fn, to clarify that it is responsible for fetching a fresh token when the cache misses or expires.