fix: don't retry when retry is disabled

[CahidArda]

Fixes #272

Summary

When HttpClient was configured with retry: false, a failing request still called fetch twice instead of once. The retry: false branch normalized to attempts: 1, but since #207 the request loop treats attempts as the number of retries after the initial attempt (index <= attempts), so 1 meant "one extra retry" rather than "one total attempt".

Changes

• Normalize retry: false to attempts: 0 in src/client/http.ts, so a disabled-retry client performs exactly one fetch attempt. Object-form semantics ({ retries: N } → N retries after the initial attempt) are unchanged.

• Add tests covering both cases: retry: false calls fetch exactly once, and { retries: 1 } calls it twice.

Testing

bun test src/client/http.test.ts — 3 pass, 0 fail (new tests plus the existing backoff-timing test).