Release Python SDK 2.0.3

[rmcdaniel]

Summary

Publish the merged worker storage-admission recovery fix from #57 as Python SDK 2.0.3. This updates package metadata and the changelog only; the protocol floor is unchanged.

Workers retain task identity, prepared payloads, and computed results across retryable storage refusals, with interruptible shutdown and terminal authentication/stale-lease failures.

Validation

• Focused storage-admission and release-metadata tests: 66 passed.
• Full public repository checks must pass before merge.
• Publish the immutable tag through the repository PyPI workflow and verify the installed artifact before treating publication as complete.

Published-artifact storage qualification is tracked in durable-workflow/server#131. No production storage-admission enablement is included.

[rmcdaniel]

Published Python SDK 2.0.3 from immutable commit 5192ccc. Publication and registry verification passed, as did the Python 3.10-3.12 matrix and Server integration checks. Local non-integration suite: 1,370 passed. The combined published storage qualification remains tracked in server#131.