.Net: Adding generic data type support to the volatile vector store.

[westey-m]

Motivation and Context

To make it easier for users to use vector stores without needing to create a data type, we need to support a generic data type that can store data for any type of record, and where the database schema is determined by the record definition.

Description

• Allow anyone using VolatileVectorStore to provide custom methods to look up vectors and keys.
• Automatically provide default implementations for regular models and the generic data model.
• Add additional validation to other existing collections for generic data types.
• Fix up tests.

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 😄