chore: cleanup and fix partial update in python

[fresh-borzoni]

cleanup and partial updates fix(discovered during writing doc):

• added latest offset for bindings
• cleaned up docstings
• fixed partial update and added example to verify

[fresh-borzoni]

@luoyuxia PTAL 🙏

[leekeiabstraction]

TY for the PR! Added small comment

[fresh-borzoni]

@leekeiabstraction TY for the review. Addressed comment. PTAL 🙏

[Copilot]

Pull request overview

This PR improves the Python bindings by fixing partial-update row handling, cleaning up row conversion utilities, and exposing a “latest offset” constant consistently across Rust core and Python.

Changes:

• Added LATEST_OFFSET constant to Rust core and exposed it in the Python module + type stubs.
• Fixed Python upsert/delete/lookup row conversion by introducing a sparse-row conversion path for partial updates and PK-only inputs.
• Updated Python typing/docs and expanded the example script with partial-update verification.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
crates/fluss/src/client/table/mod.rs	Adds LATEST_OFFSET constant in the core client table module.
bindings/python/src/lib.rs	Exposes LATEST_OFFSET to Python via the extension module.
bindings/python/src/upsert.rs	Stores/resolves partial-update target columns and uses sparse row conversion for partial upserts + PK deletes.
bindings/python/src/table.rs	Refactors row conversion into python_to_sparse_generic_row and reuses it for full-row conversion.
bindings/python/src/lookup.rs	Uses sparse row conversion for PK lookups.
bindings/python/fluss/init.pyi	Updates stubs/docs: supported types list + adds LATEST_OFFSET.
bindings/python/example/example.py	Adds example code to verify partial update behavior by names and indices.

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