refactor renaming agent base - 4667

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Why are these changes needed?

small refactoring. Doesn't need to be named AgentBase, Its an agent and the class is abstract.

Related issue number

closes #4667

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

Copilot reviewed 5 out of 13 changed files in this pull request and generated 1 suggestion.

Files not reviewed (8)

• dotnet/samples/Hello/HelloAgent/Program.cs: Evaluated as low risk
• dotnet/samples/Hello/HelloAgentState/Program.cs: Evaluated as low risk
• dotnet/src/Microsoft.AutoGen/Agents/AgentBase.cs: Evaluated as low risk
• dotnet/src/Microsoft.AutoGen/Agents/AgentBaseExtensions.cs: Evaluated as low risk
• dotnet/src/Microsoft.AutoGen/Agents/AgentRuntime.cs: Evaluated as low risk
• dotnet/src/Microsoft.AutoGen/Agents/Agents/AIAgent/InferenceAgent.cs: Evaluated as low risk
• dotnet/src/Microsoft.AutoGen/Agents/Agents/AIAgent/SKAiAgent.cs: Evaluated as low risk
• dotnet/src/Microsoft.AutoGen/Agents/Agents/IOAgent/IOAgent.cs: Evaluated as low risk

Comments skipped due to low confidence (3)

dotnet/src/Microsoft.AutoGen/Agents/Services/HostBuilderExtensions.cs:21

• [nitpick] The generic type parameter TAgent should be renamed to TAgentBase to reflect the fact that it is constrained to types derived from Agent.

[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TAgent>(this IHostApplicationBuilder builder, string typeName) where TAgent : Agent

dotnet/src/Microsoft.AutoGen/Agents/Services/Grpc/GrpcAgentWorker.cs:197

• The cast to Agent may cause a runtime error if agentType does not inherit from Agent. Ensure that all agent types in _agentTypes inherit from the Agent class.

agent = (Agent)ActivatorUtilities.CreateInstance(_serviceProvider, agentType, context);

dotnet/src/Microsoft.AutoGen/Agents/Services/AgentWorker.cs:200

• Casting to the new 'Agent' class may cause runtime issues if there are still references to 'AgentBase' elsewhere. Ensure all instances of 'AgentBase' are updated to 'Agent'.

agent = (Agent)ActivatorUtilities.CreateInstance(_serviceProvider, agentType, context);