.NET: [BREAKING] Subclass AgentThread so that different agents have their own threads with their own typed settings. (#798)

* Subclass AgentThread so that different agents have their own threads with their own typed settings.

* Address PR comment.

* Add unit tests for base abstract threads

* Fix style warning

* Fix stlying

* FIx and suppress warnings as needed.

* Remove covariant thread response types and fix some styling.

* Remove unecessary json property name attributes and make OrchestratingAgentThread private

* Fix break from merge from main.

* Fix formatting

* Fix deserialization bug in Memory sample

* Remove thread deletion from basic samples.

* Remove public constructors for thread subclasses and add more factory methods to concrete agent types.

* Update AgentProxy thread constructors to be internal as well.

* Revert AgentProxyThread to internal

* Change AIContextProvider to internal set

* Change conversation id and message store properties to internal set

* Update styling.

* Seal various thread types.

* Add thread type check for thread deletion

* Fix tests after latest merge from main

* Add thread type checks for thread deletion.

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Co-authored-by: Chris <66376200+crickman@users.noreply.github.com>

dotnet/samples/GettingStarted/AgentOpenTelemetry/Program.cs

@@ -123,7 +123,7 @@ appLogger.LogInformation("Agent created successfully with ID: {AgentId}", agent.
 
 // Create a parent span for the entire agent session
 using var sessionActivity = activitySource.StartActivity("Agent Session");
-var sessionId = thread.ConversationId ?? Guid.NewGuid().ToString();
+var sessionId = Guid.NewGuid().ToString();
 sessionActivity?
     .SetTag("agent.name", "OpenTelemetryDemoAgent")
     .SetTag("session.id", sessionId)