Annotate typing

[FabianHofmann]

Add type annotations & add MyPy to pre-commit hooks. This is quite a large change, but the functional change is kept to a minimum.

closes #303 closes #185

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 87.84091% with 107 lines in your changes missing coverage. Please review.

Project coverage is 88.29%. Comparing base (3d2a72b) to head (201b164). Report is 3 commits behind head on master.

:exclamation: Current head 201b164 differs from pull request most recent head 5949eca

Please upload reports for the commit 5949eca to get more accurate results.

Files	Patch %	Lines
linopy/expressions.py	90.15%	12 Missing and 7 partials :warning:
linopy/model.py	87.03%	9 Missing and 5 partials :warning:
linopy/solvers.py	85.05%	8 Missing and 5 partials :warning:
linopy/variables.py	91.15%	9 Missing and 4 partials :warning:
linopy/io.py	81.25%	6 Missing and 6 partials :warning:
linopy/common.py	81.66%	6 Missing and 5 partials :warning:
linopy/constraints.py	91.13%	2 Missing and 5 partials :warning:
linopy/constants.py	66.66%	3 Missing and 2 partials :warning:
linopy/matrices.py	87.09%	2 Missing and 2 partials :warning:
linopy/types.py	82.60%	3 Missing and 1 partial :warning:
... and 2 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #310 +/- ## ========================================== - Coverage 89.72% 88.29% -1.43% ========================================== Files 16 17 +1 Lines 4037 4159 +122 Branches 942 978 +36 ========================================== + Hits 3622 3672 +50 - Misses 282 316 +34 - Partials 133 171 +38 ```

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[FabianHofmann]

@lkstrp could I kindly ask you to take over fixing the pre-commit bot. It looks like the pre-commit CI is sort of stuck with another set of (cached ?) arguments. Locally it works fine. What I want in the end is to run mypy checks on linopy/ and test/

[FabianHofmann]

@lkstrp awesome thanks