[python][ray] Incrementally commit update_by_row_id file groups

[XiaoHongbo-Hope]

Purpose

• Add an opt-in max_groups_per_commit parameter to update_by_row_id.
• Deliver completed _FIRST_ROW_ID file groups to the driver as Ray workers finish, and commit each bounded window through a reusable StreamTableCommit.
• Keep the existing single atomic commit behavior when the option is unset.
• Preserve the original base snapshot on every commit message so conflict detection still covers the full read-to-commit window.
• Document that incremental mode may leave earlier windows committed if a later window fails.

Tests

• pytest -q pypaimon/tests/ray_update_by_row_id_test.py pypaimon/tests/table_merge_into_test.py pypaimon/tests/table_update_test.py (138 passed, 16 subtests passed)
• Multi-worker Ray coverage with 8 input blocks, 4 shuffle partitions, 8 file groups, and 3 groups per commit.
• flake8 --config=dev/cfg.ini on changed Python files.
• Python 3.6 py_compile compatibility check.
• git diff --check.