fix: retry per-attempt timeouts and validate vector dimensions

[TheGreatAxios]

Summary

• A per-attempt timeoutMs expiry is classified as timeout, which the default retry policy retries; a caller signal abort is still aborted and not retried.
• embedTexts rejects empty vectors, vectors whose length differs from the first in the same call (across batches), and vectors whose length differs from config.dimensions when set. Each throws EmbeddingRequestError with protocol_mismatch.
• README: timeoutMs and dimensions rows and the Dimensions section describe the new behavior.
• Stacked on chore: align repo scaffolding with the package standard #17.

Verification

• bun run check, bun run build: pass
• bun run test:e2e with EMBEDDING_E2E_BASE_URL=http://100.113.184.123:11434/v1: 12 pass, 0 fail (live included)
• New tests (timeout retried then succeeds; timeout exhausts 3 attempts as timeout; caller abort stays aborted; empty, uneven and off-dimension vectors) failed before the fix, except the caller-abort guard
• Node pack smoke: pass

Closes CL-9445