async user hook support added

[robraux]

Why are these changes needed?

• Async user hooks are added to mirror library async support in other areas.
• Adds async tests for all hook types, adds sync tests for 2 untested hook types.
• Adds hook sync vs. async checks on add hook, with warning for mismatch

Related issue number

Closes/replaces: #1845

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.

[robraux]

Tagging you @rickyloynd-microsoft, @gagb, and @cemtu as you commented previously on the hung PR #1845

[ekzhu]

LGTM