[ISSUE-137] Python bindings row-based append API

[fresh-borzoni]

Purpose

Linked issue: close #137

Adds a Python append() method to enable single-row inserts with support for dict, list, and tuple input formats, providing a more ergonomic API for appending individual rows compared to batch operations.

Brief change log

• Add append() method to Python Table class with support for dict, list, and tuple input
• Implement RowInput enum with FromPyObject derive for automatic type dispatch
• Add python_to_generic_row() function to convert Python values to GenericRow with strict validation
• Add python_value_to_datum() function with type-specific conversions, optimized bytes extraction, and field-level error messages
• Add Python patterns to .gitignore to exclude __pycache__/ and *.so files
• Add usage examples and type stubs for the new API

API and Format

API Changes: Yes

• New public method: Table.append(row) accepting dict | list | tuple
• Blocking operation (releases GIL during execution)

Storage Format: No changes

Documentation

New Feature: Yes

• Added docstring with examples for dict, list, and tuple input
• Added type stubs in __init__.pyi
• Added usage examples in example/example.py

[fresh-borzoni]

@luoyuxia PTAL, when comfortable 🙏

[Copilot]

Pull request overview

This PR adds a row-based append API to Python bindings, enabling single-row inserts with support for dict, list, and tuple input formats. This provides a more ergonomic alternative to batch operations for streaming use cases and real-time ingestion.

Changes:

• Added append() method to AppendWriter class supporting dict, list, and tuple input formats
• Implemented type conversion logic from Python values to Fluss Datum types with strict validation
• Added Python patterns to .gitignore to exclude build artifacts

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
bindings/python/src/table.rs	Adds append() method, row input conversion logic, and Python-to-Datum type mapping with validation
bindings/python/fluss/init.pyi	Adds type stubs and comprehensive documentation for the new append() method
bindings/python/example/example.py	Demonstrates usage of new append() API with dict and list inputs
.gitignore	Adds Python-specific ignore patterns for build artifacts

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