fix: type browser pool acquire timeout as null

[Sayan-]

Summary

Type browserPools.acquire() as returning a browser or null. The SDK already parses HTTP 204 as null; the return type now reflects that long-poll outcome without changing API behavior or adding automatic retries.

Validation

Added mock response tests for 200, 204, and 404, including a check that 204 does not trigger an automatic retry. All 3 focused tests passed, and TypeScript type checking passed.

The change was not exercised against a live pool.

The SDK's separate 60-second request timeout can still expire before a longer API poll reaches 204.

Generation and release

This custom SDK change targets next, the branch used for the versioned release PR. After that release reaches main, production changes must back-sync to SDK staging and the next stlc build must preserve this behavior. Merge the resulting custom-code tracking PR in the API configuration repo before relying on a later generation. The API's existing OpenAPI contract already documents the 200, 204, and 404 outcomes.

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Note

Low Risk
Type-only alignment with existing 204→null parsing plus tests; callers may need explicit null checks at compile time.

Overview
Updates the TypeScript return type of browserPools.acquire() to BrowserPoolAcquireResponse | null, matching existing runtime behavior where a long-poll HTTP 204 (no browser available within the wait window) is already parsed as null. No request/retry logic changes.

Adds focused API tests for 200 (session payload), 204 (null and a single fetch call), and 404 (NotFoundError).

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