CHORE: e2e bulk copy into a CLR UDT column (GH-667)

[gargsaumya]

Adds an end-to-end bulkcopy test for CLR UDT columns (GH-667).

Summary

What

test_bulkcopy_udt_geometry seeds a geometry column, reads the serialized UDT bytes back, bulk copies them into a second geometry column, and asserts a byte-exact round-trip (including a NULL row).

The built-in geometry CLR UDT travels the identical TDS 0xF0 wire path as custom UDTs (which require a deployed assembly, impractical in CI), so it faithfully exercises the fixed path.

Why

Before the fix, cursor.bulkcopy() into any UDT column failed - first with a malformed varbinary(-1) / Unsupported TDS type for bulk copy: 0xF0, and (once the wire mapping was fixed) with a target SQL type is Udt value-coercion error.

Dependency

This test requires the GH-667 fix in mssql_py_core (microsoft/mssql-rs#111), which contains two parts:

1. mssql-tds: map UDT to varbinary(max) for the bulk-copy wire type / COLMETADATA / statement text.
2. mssql-py-core: accept bytes -> UDT in bulk-copy value coercion.

Validated locally end-to-end against SQL Server with a py-core built from that branch. This should land together with the mssql-py-core version bump that ships the fix (the maintainers will handle the bump).

Related: microsoft/mssql-rs#111 · Fixes #667

[Copilot]

Pull request overview

Adds an end-to-end regression test to validate that cursor.bulkcopy() can insert CLR UDT values (via the built-in geometry type) by round-tripping the UDT’s serialized bytes, covering both non-NULL and NULL rows. This extends the bulkcopy integration suite to exercise the TDS 0xF0 (UDT) wire path via mssql_py_core.

Changes:

• Add test_bulkcopy_udt_geometry to seed geometry values, fetch their serialized form, bulk copy into a second geometry column, and assert byte-exact equality.
• Ensure the test explicitly covers a NULL row alongside non-NULL UDT values.