test: add type hints to test_model

[tonyandrewmeyer]

• One change to ops/charm, but only in the type hints. It looks from the use of Required that the other fields are not meant to be required, so make that the case (this also appears to match the code).
• Ignore types in the tests that are checking that bad types are handled properly.
• Help type checkers understand when some optional attributes won't be None.
• Replace a few bits of code where a minimal object was passed, enough for the test to do it's check, but not of the correct type, with an actual object of the proper type.
• Sprinkle type hints where required for pyright to understand what's happening.

Partially addresses #1007

[benhoyt]

Nice work! Left a bunch of suggestions to simplify / clean a few things up.

[benhoyt]

Thanks for the updates! I won't merge this until you make a final decision on those last outstanding comments -- your call as to whether to use typing.Any or whatever there, or keep the annotations.