chore: enable mypy strict mode

[gruebel]

This PR

• most of the type hint changes are pretty straight forward
• one check of the strict checks is disabled to keep this PR rather small
• changed a list-filter-lambda combo to a list comprehension, because mypy tripped on it and in general list comprehension are more performant compared to such a combo
• also enabled mypy pretty mode, which gives quite nice error outputs ex.

  
  openfeature/hook/hook_support.py:52: error: Missing type parameters for generic
  type "Mapping"  [type-arg]
      hints: typing.Optional[typing.Mapping] = None,
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (30f4e69) 93.83% compared to head (b833562) 93.84%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #257 +/- ## ========================================== + Coverage 93.83% 93.84% +0.01% ========================================== Files 16 16 Lines 438 439 +1 ========================================== + Hits 411 412 +1 Misses 27 27 ``` | [Flag](https://app.codecov.io/gh/open-feature/python-sdk/pull/257/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-feature) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/open-feature/python-sdk/pull/257/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-feature) | `93.84% <100.00%> (+0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-feature#carryforward-flags-in-the-pull-request-comment) to find out more.

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[federicobond]

Apparently one of the lint rules for ruff conflicts with the mypy configuration:

openfeature/_backports/strenum.py:5:22: PLC0414 Import alias does not rename original package

[gruebel]

@federicobond strange I thought I ran ruff multiple times 🤔 will ignore the rule in this specific line, because there is no other way I know to make both mypy and ruff happy. I prefer mypy to be happy 😄