[TASK-167] Support Arrow append operations for decimals, temporal types

[fresh-borzoni]

Linked issue: close #167

Add Date, Time, Timestamp (NTZ/LTZ), and Decimal type support to Python bindings' append() method.

Brief change log

• Add type converters for datetime.date, datetime.time, datetime.datetime, and decimal.Decimal in table.rs
• Fix Arrow-to-Fluss type mapping with correct precision for Time32/Time64 and Timestamp types
• Route Arrow Timestamp(unit, Some(tz)) → TimestampLtz, Timestamp(unit, None) → TimestampNtz
• Fix write_pandas() to pass expected schema for proper type casting
• Update example with new types demonstration

[fresh-borzoni]

@leekeiabstraction @luoyuxia PTAL 🙏

[leekeiabstraction]

Thank you for the PR! Left some comments.

[fresh-borzoni]

@leekeiabstraction Thank you for the review.
Addressed comments. PTAL 🙏

[Copilot]

Pull request overview

This PR adds support for temporal types (Date, Time, Timestamp NTZ/LTZ) and Decimal types to the Python bindings' append() method. It enables users to write these types directly from Python datetime objects and decimal.Decimal to Fluss tables.

Changes:

• Added Arrow-to-Fluss type mapping with precision-aware conversions for Time32/Time64 and Timestamp types
• Implemented Python-to-Datum converters for datetime.date, datetime.time, datetime.datetime (both naive and timezone-aware), pandas.Timestamp, and decimal.Decimal
• Enhanced write_pandas() to pass expected schema for proper type casting
• Updated example to demonstrate new type support

Reviewed changes

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

File	Description
bindings/python/src/utils.rs	Added precision-aware Arrow-to-Fluss type mappings for Time32/Time64 and Timestamp types, with timezone-based routing for TimestampLtz vs Timestamp NTZ
bindings/python/src/table.rs	Implemented comprehensive type converters for temporal and decimal types, including time conversion constants, caching mechanisms, and helper functions for Python type conversions
bindings/python/example/example.py	Updated example to demonstrate Date, Time, Timestamp, and Decimal type usage with both Arrow and row-level append operations
bindings/python/Cargo.toml	Added bigdecimal 0.4 dependency for Decimal type support

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The constant MICROS_PER_MILLI is being used as both the modulo divisor and as a conversion factor from microseconds to nanoseconds. While numerically correct (both are 1000), this is semantically confusing. Consider using a more appropriately named constant for the conversion factor, such as NANOS_PER_MICRO, or use a literal 1000 for clarity. This would improve code readability and make the intent clearer.

[Copilot]

For consistency with the rest of the code that uses named constants for time conversions (lines 29-35), this magic number should be replaced with a named constant. Consider using the existing NANOS_PER_MILLI constant divided by MICROS_PER_MILLI, or defining a new constant NANOS_PER_MICRO = 1000.