.Net: Add shared integration tests for checking vector search scores

[westey-m]

Motivation and Context

Adds tests for verifying the scores as mentioned in #10103
Only adding tests for passing connectors right now.

Description

Adding a common base test class with integration tests for checking the returned vector scores.
Adding subclasses for InMemory, Qdrant and Postgres, since these are passing end to end.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄