[Python] Fail bundles on state write errors

[bvolpato]

A runner-reported append or clear failure can currently complete a Python bundle successfully because runtime state commits ignore StateResponse.error. A clear followed by an append also loses the clear response.

Check every pending write response before completing bag, set, and ordered-list state commits, and preserve both futures for clear-then-append. Regression tests cover failed appends and clears, multiple append chunks, set compaction, and successful commits. The new tests fail against the upstream implementation.

Testing

From sdks/python, with the SDK and test dependencies installed:

python -m pytest apache_beam/runners/worker/bundle_processor_test.py apache_beam/runners/worker/sdk_worker_test.py -q

Python 3.12: 45 passed, plus 15 subtests passed. The new regression cases produced 15 failures against the unfixed implementation. YAPF 0.43.0, Ruff 0.15.22, and git diff --check pass for the changed files.

Downsides

Previously hidden backend failures now fail the bundle and invoke the runner's existing failure/retry handling. The successful path adds no state RPCs. Retry uses the existing runner contract that failed state handlers must not reuse their cache token.

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• Describe the bug and include a reproducible regression test; no separate Python issue is linked.
• Update CHANGES.md with the behavior change.
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