Arrow ADBC: Primary Key and Foreign Key Metadata Optimization

Description

This PR adds support for optimizing Primary Key and Foreign Key metadata queries in the C# Databricks ADBC driver. It introduces a new connection parameter adbc.databricks.enable_pk_fk that allows users to control whether the driver should make PK/FK metadata calls to the server or return empty results for improved performance.

Background

Primary Key and Foreign Key metadata queries can be expensive operations, particularly in Databricks environments where they may not be fully supported in certain catalogs. This implementation provides a way to optimize these operations by:

1. Allowing users to disable PK/FK metadata calls entirely via configuration
2. Automatically returning empty results for legacy catalogs (SPARK, hive_metastore) where PK/FK metadata is not supported
3. Ensuring that empty results maintain schema compatibility with real metadata responses

Proposed Changes

• Add new connection parameter adbc.databricks.enable_pk_fk to control PK/FK metadata behavior (default: true)
• Implement special handling for legacy catalogs (SPARK, hive_metastore) to return empty results without server calls
• Modify method visibility in base classes to allow proper overriding in derived classes
• Add comprehensive test coverage for the new functionality

How is this tested?

Added unit tests that verify:

1. The correct behavior of the ShouldReturnEmptyPkFkResult method with various combinations of settings
2. Schema compatibility between empty results and real metadata responses
3. Proper handling of different catalog scenarios

These tests ensure that the optimization works correctly while maintaining compatibility with client applications that expect consistent schema structures.