Replace Buffer with Uint8Array, drop buffer dependency

[Arechii]

Summary

• Migrate the public API and internals from Node Buffer to browser-native Uint8Array. Frame is now Uint8Array | string and emitted frames are Uint8Array. Since Buffer extends Uint8Array, code that passed Buffer values keeps working, but consumers calling Buffer-only methods (readUInt8, toString('hex'), writeInt32BE, etc.) on emitted frames will need to migrate.
• Drop the buffer npm dependency entirely so browser bundles no longer ship the ~50 kB Node Buffer polyfill.
• Add a small src/utils/bytes.ts helper (concatBytes, encodeUtf8, bytesToHex) used by webSocketEndpoint, sub/xsub/xpub, and router.
• Bump version to 0.3.0, add lib: ["es2018", "dom"] and skipLibCheck to tsconfig.json to pick up TextEncoder typing.

Why

Browser consumers of @blueyerobotics/jszmq (and downstream @blueyerobotics/blueye-ts) currently ship the ~50 kB buffer polyfill on Vite to satisfy Buffer.from/concat/isBuffer. With Vite 8 the popular vite-plugin-node-polyfills plugin emits a deprecation warning on every build (it still uses the old esbuild config rather than oxc) and is unmaintained on the Vite-8 transition. Stripping Buffer from this library eliminates the need for any Node compat shim.

Tracking issue: BluEye-Robotics/blueye-ts#6.

Notable changes

• src/types.ts: Frame = Uint8Array | string; IEndpoint.routingKey: Uint8Array.
• src/webSocketEndpoint.ts: send() runtime check is now frame instanceof Uint8Array; Buffer.alloc → new Uint8Array; readUInt8(0) → [0]; slice(1) → subarray(1); Buffer.from(arrayBuffer) → new Uint8Array(arrayBuffer).
• src/router.ts: routing-key generation now uses DataView.setInt32(..., false) for the BE 32-bit ID; map keys use bytesToHex instead of Buffer.toString('hex').
• src/sub.ts, src/xsub.ts, src/xpub.ts, src/utils/trie.ts, src/utils/multiTrie.ts: all Buffer.* calls replaced with Uint8Array equivalents.
• src/index.ts: drop export {Buffer} from 'buffer'.

Test plan

• pnpm build passes
• pnpm test — 5/5 specs pass (pubsub subscribe/unsubscribe, dealer-router ping-pong, reqrep simple + 100x stress)
• grep -rn "Buffer\." lib returns no matches
• grep -rn "require(\"buffer\")\|require('buffer')" lib returns no matches
• Smoke-test downstream @blueyerobotics/blueye-ts against this build (will follow up in that repo's PR)

Breaking changes

• Public type widening: Frame = Uint8Array | string instead of Buffer | string. Source-compatible for callers passing Buffer.
• Emitted frames are typed as Uint8Array (still Buffer instances at runtime when used in Node, since Buffer extends Uint8Array). Consumers calling Buffer-specific methods on received frames must switch to:
  • frame.toString('utf8') → new TextDecoder().decode(frame)
  • frame.readUInt8(0) → frame[0]
  • frame.toString('hex') → use a hex helper (or bytesToHex exported from this lib if we want to expose it)
• export {Buffer} from 'buffer' removed from index.ts. Consumers re-importing Buffer from this package should import it from 'buffer' (or use Uint8Array directly).

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