Add runtime VectorData compatibility canary test

[BenjaminMichaelis]

Why

Production chat streaming is currently failing with a runtime MissingMethodException from the PgVector search path (VectorSearchOptions<T>.get_OldFilter()), which indicates package binary incompatibility that was not being caught by tests.

What changed

• Reworked PgVectorConnectorTests to validate runtime VectorData compatibility through the real connector search path.
• Renamed the test to GetCollection_WithBookContentChunk_RuntimeVectorDataApiShapeIsCompatible to reflect intent.
• After creating the collection, the test executes SearchAsync(...) with VectorSearchOptions<BookContentChunk> and advances the async enumerator.
• The current package graph causes this test to fail with the same MissingMethodException, creating the requested red baseline.

Notes for reviewers

• This is an intentional canary/regression gate: it is expected to fail until NuGet package versions are aligned.
• Once package alignment is fixed, this same test should pass without test changes.