[core] Add confirmed snapshot commit callbacks

[JingsongLi]

Why

PyPaimon already supports commit callbacks, but registering one currently forces its REST commit path back to Python because Rust core cannot deliver a post-publication notification.

Changes

• Add CommitCallback and CommitCallbackContext to Rust core. Context contains the confirmed snapshot, its data-file delta and the commit identifier, including assigned row IDs and sequence numbers.
• Notify in registration order only after confirmed publication. Recover notifications from persisted delta manifests after a lost publication response, retaining file statistics.
• Propagate callback errors while preserving published data and metadata. Callback failures stop later callbacks and do not republish the snapshot.
• Expose public add_commit_callback(callback) on the Python batch and stream committers. Callbacks receive a typed, retainable CommitCallbackContext wrapping core snapshot, manifest entries, file metadata and statistics. Preserve original Python exceptions and allow Native reads inside callbacks.
• Keep the existing Java v14 bridge and Snapshot JSON conversion internal to the PyPaimon adapter; neither is part of the public callback signature.
• Make callback references visible to Python GC and release them on close. Cover callback-owner cycles with both explicit close and abandoned committers.

The notification timing and data-file delta follow Java FileStoreCommitImpl / CommitCallback.Context. The exposed context covers existing PyPaimon capabilities. Java's separate checkpoint retry(committable) hook is outside this change; filtering already committed identifiers does not emit a notification. Format Tables have no Paimon snapshots and reject registration.

Python binding API

commit.add_commit_callback(lambda context: print(
    context.identifier,
    context.snapshot.id(),
    [entry.file.file_name for entry in context.commit_entries],
))

The context and metadata views are read-only and can be retained after the callback returns. Callback ownership remains with the caller; the native committer releases its Python reference on close.

Verification

• cargo test -p paimon --lib table::table_commit::tests --locked: 125 passed.
• Python binding test_table_commit.py: 71 passed.
• PyPaimon Native write / commit / callback integration: 187 passed against this branch's locally built extension.
• Rust 1.98.0 formatting and workspace Clippy with fulltext,vortex and -D warnings: passed.
• Independent reviews of core publication/recovery and Python bridge/resource ownership completed; the GC finding was fixed and revalidated.

The dependent PyPaimon PR apache/paimon#10509 retains the existing public callback API and continue building Rust main in CI.

[leaves12138]

LGTM. I reviewed the confirmed-publication callback flow, lost-response recovery from persisted delta manifests, row-tracking metadata assignment, overwrite/delete entries, callback error propagation, and Python callback resource ownership. The targeted Rust suite passed (125 tests), and all Rust PR checks are green.