Updated type hints for Agent Capabilities

[Hk669]

Why are these changes needed?

I've updated the type hints of the Teachability and MemoStore to improve code readability, maintainability, and to facilitate static type checking. This enhancement will make it easier for developers to understand the expected types of parameters and return values, reducing the likelihood of type-related errors and improving overall code quality.

Related issue number

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]

@sonichi please review the PR.