.Net: Initial pass for native aot annotations for inmemory connector.

[azchohfi]

Motivation and Context

Microsoft.SemanticKernel.Connectors.InMemory warns if using NativeAOT.
This PR contributes to #10256, and helps make SK NativeAOT compatible.

Description

In the InMemory project, I've turned PublishAot to true, then built the project.
This shows a number of warnings. This PR solves all of those warning but the JsonSerializer ones, that are part of a longer discussion in the linked issue. The solution is to simply annotate the calling methods/types/generic definitions with the suggested attributes, which now bubble up to any possible callers, allowing the linker to not remove some specific methods/ctors.

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 😄