.NET: Rename AgentRunResponse{Update} to AgentResponse{Update}

[qmuntal]

Having the Run word in AgentRunResponse and AgentRunResponseUpdate makes those types unnecessary verbose. In my opinion, AgentResponse and AgentResponseUpdate convey the same information while being a bit shorter.

I get that Run was introduced to make it clear that it is the response from an AIAgent.Run* function, but the whole point of an agent is to run it with some messages, so AgentResponse should be clear enough. Also, AgentRunResponse{Update} is not only returned by AIAgent.Run* functions; middlewares and and other helper classes can return it from functions that don't have the Run word on it.

Note that this follows the ChatResponse{Update} pattern, which doesn't contain the Get verb to tie the result with the IChatClient.GetResponse* functions.

[SergeyMenshykh]

CC: @eavanvalkenburg, @TaoChenOSU for same change on Python side.