fix: update cohere tool calling multi agents

[Anirudh31415926535]

Why are these changes needed?

There is an issue whereby tool_results could be passed to the model when it actually doesn't have any tools in the meta router agent. This causes some issues with the raw prompts seen by the model.

Another major issue is that the sub-agent names are not present in messages. Adding the sub agent names as prefix to message content.

Plus some minor bug fixes.

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.

[Hk669]

@Anirudh31415926535 can you please explain the changes briefly.

[Anirudh31415926535]

@Anirudh31415926535 can you please explain the changes briefly.

Hi @Hk669 I've updated the description! Would it be possible to have a review? Thanks! :)

[Anirudh31415926535]

@Hk669 Hi there, may I please check if we could get a review on this? This PR is blocking us to use autogen for an important enterprise use case! Would really appreciate a review so that we can merge this asap! Thanks! :)