[python] Add commit support for resumable row-id updates

[XiaoHongbo-Hope]

Depends on #8826.

This adds the remaining commit primitives needed by resumable row-id writers:

• read live entries intersecting planned row-id ranges;
• verify planned target files are still live before commit;
• attach checkpoint properties and create metadata-only stream commits.

Tests: commit scanner/conflict and table commit suites; project flake8 clean.

[XiaoHongbo-Hope]

Closing this draft because the current direction is the standalone time-based incremental write_paimon implementation in #9033. #9033 includes the minimal snapshot-property, metadata-commit, and conservative conflict guards it needs directly on master; the row-id-specific guards in this stacked PR are no longer required.