FEAT: Support for Apache Arrow in Bulk Copy API (#665)

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[AB#46268](https://sqlclientdrivers.visualstudio.com/c6d89619-62de-46a0-8b46-70b92a84d85e/_workitems/edit/46268)

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### Summary   
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This pull request introduces a new high-performance `bulkcopy_arrow`
method to the `Cursor` class for bulk loading data directly from Apache
Arrow sources, along with several related improvements and refactorings.
It also updates type stubs and documentation to reflect the new API, and
improves bulk copy authentication handling by refactoring shared logic.

**New feature: Arrow-based bulk copy**

* Added `Cursor.bulkcopy_arrow(table_name, source)` for efficient bulk
loading from Arrow sources (e.g., `pyarrow.Table`, `RecordBatch`,
objects exposing the Arrow C Data Interface). This avoids unnecessary
Python row materialization and is significantly faster for Arrow-native
data.
[[1]](diffhunk://#diff-06572a96a58dc510037d5efa622f9bec8519bc1beab13c9f251e97e657a9d4edR12-R23)
[[2]](diffhunk://#diff-deceea46ae01082ce8400e14fa02f4b7585afb7b5ed9885338b66494f5f38280R3175-R3338)
* The classic `bulkcopy()` method now raises a `TypeError` if given
Arrow-shaped data, steering users to the new method.

**Codebase refactoring and improvements**

* Refactored connection context and Azure AD authentication logic into a
shared `_build_pycore_context()` helper, used by both `bulkcopy` and
`bulkcopy_arrow`. This ensures consistent authentication handling and
reduces code duplication.
[[1]](diffhunk://#diff-deceea46ae01082ce8400e14fa02f4b7585afb7b5ed9885338b66494f5f38280R2818-R2942)
[[2]](diffhunk://#diff-deceea46ae01082ce8400e14fa02f4b7585afb7b5ed9885338b66494f5f38280L2940-R3076)
* Updated type stubs (`mssql_python.pyi`) to include the new
`bulkcopy_arrow` method and improved the typing for `bulkcopy`.
[[1]](diffhunk://#diff-8b251a7d56f9bb22b686d2b101b0420b1d6cd6934b29edcd408c1f579f7d9e84L7-R7)
[[2]](diffhunk://#diff-8b251a7d56f9bb22b686d2b101b0420b1d6cd6934b29edcd408c1f579f7d9e84R212-R241)

**Documentation**

* Updated the `CHANGELOG.md` to document the new Arrow bulk copy feature
and its requirements.

**Minor improvements**

* Minor code formatting improvement in a test file
(`test_bulkcopy_udt_geometry`).
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Author: gargsaumya

CHANGELOG.md

@@ -9,6 +9,18 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Added
 - New feature: Support for macOS and Linux.
 - Documentation: Added API documentation in the Wiki.
+- **GH-570:** New `Cursor.bulkcopy_arrow(table_name, source)` method for
+  high-performance bulk loading directly from Apache Arrow data. Accepts a
+  `pyarrow.Table`, `RecordBatch`, or `RecordBatchReader`, any object exposing
+  the Arrow C Data Interface (`__arrow_c_stream__` / `__arrow_c_array__` — e.g.
+  polars, pandas 2.2+, DuckDB, ADBC results), or an iterable of record batches.
+  Data is streamed to the server through the Arrow C Data Interface without
+  materializing intermediate Python row objects, and the GIL is released for
+  the duration of the network transfer. When the source data already originates
+  as Arrow, this avoids the Arrow→tuple conversion the classic `bulkcopy()`
+  path requires (measured ~1.4x–2.7x faster end-to-end for such sources).
+  `bulkcopy()` now raises `TypeError` steering Arrow inputs to this method.
+  Requires `mssql-py-core` 0.1.5+.
 - Bulk copy now supports `Authentication=ActiveDirectoryServicePrincipal`
   via an `entra_id_token_factory` callback registered on the mssql-py-core
   connection. The callback is invoked by mssql-tds mid-handshake (FedAuth