FIX: Update time handling in Arrow integration to include fractional seconds

[ffelixg]

Work Item / Issue Reference

GitHub Issue: #498

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Summary

Map SQL time types to the arrow nanosecond type and include the fraction part of SQL_SS_TIME2_STRUCT in the value calculation.

For consistency, also remove the unreachable SQL_TIME and SQL_TYPE_TIME branches.

[Copilot]

Pull request overview

Updates the Arrow fetch integration to preserve SQL Server TIME fractional seconds by representing time columns as Arrow time64(ns) and computing values using the full SQL_SS_TIME2_STRUCT (including fraction).

Changes:

• Map SQL_SS_TIME2 columns to Arrow C Data interface format ttn (time64 in nanoseconds) and store values in an int64_t nanosecond buffer.
• Include SQL_SS_TIME2_STRUCT.fraction in the computed time value (nanoseconds since midnight).
• Update Arrow integration tests to expect pa.time64("ns") and add a fractional-seconds time(7) test case; remove the Parquet workaround that was specific to time32("s").

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tests/test_004_cursor_arrow.py	Updates expected Arrow time types to time64(ns), adds a fractional time(7) case, and simplifies the Parquet roundtrip validation.
mssql_python/pybind/ddbc_bindings.cpp	Switches Arrow time backing storage to nanoseconds (int64_t) and includes fractional seconds when materializing Arrow time values.

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