Add runtime type checking

[DimitriPapadopoulos]

Is your feature request related to a problem?

Runtime type checking in CI tests may provide the "automated way of checking" suggested at the end of #9581.

Describe the solution you'd like

Add pytest-beartype to CI tests.

Describe alternatives you've considered

No response

Additional context

I expect this:

• may detect new typing issues beyond static type checking,
• will detect TYPE_CHECKING misuse possibly introduced by the likes of Enforce ruff/flake8-type-checking rules (TCH) #9728.

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