Swarm tests and bug fixes

[marklysze]

Why are these changes needed?

Implementation of tests for swarms.

Includes a number of bug fixes for swarms as well:

• Multiple tool calling where context variables are updated in each
• Matching name for the initial message

Added a number of type checks as well.

Related issue number

Checks

• I've included any doc changes needed for https://ag2ai.github.io/ag2/. See https://ag2ai.github.io/ag2/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.

[marklysze]

@yiranwu0, thanks so much for testing. Can you have another look over please.

[marklysze]

Note: OpenAI tests passed, except for one that retrieves the latest news (which contained some restricted words for Azure and its content filter was triggered). So will merge on that basis.