.Net: Add integration test to ensure that search only embedding generation works

[westey-m]

Motivation and Context

We should be able to use an embedding generator to search even when we provide vectors for upsert directly.

Description

• Adds a conformance test to verify this behavior.
• The test is currently failing for all implementations, as we require a fix.

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 😄