…age. (microsoft#7154)

### Motivation and Context

We have mypy enabled on parts of the code base, but not all. The goal is
to enable it across the entire SK python code. As part of this, we've
broken up the work to tackle different sections. Additionally, we're
working to improve the code coverage for these sections of code.

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### Description

This PR:
- turns on mypy for the function choice behavior code. Code adjustments
were made per mypy, with the exclusion of one place that contain a
`type: ignore` as mypy claimed the function mapping couldn't execute
properly, when it indeed can.
- adds more unit test coverage for the function choice behavior and
class and classmethods. There is 100% code coverage.
- fixes a bug related to mapping the function call behavior required
behavior to the new required behavior.
- closes microsoft#7137

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### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [X] The code builds clean without any errors or warnings
- [X] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [X] All unit tests pass, and I have added new tests where possible
- [X] I didn't break anyone 😄