Gradually introduce type checking

[nebfield]

Now we're using a lot of type hints with pydantic, it would be sensible to enforce checking them with mypy

mypy has been configured to be pretty relaxed:

• Only check pgscatalog.core to start with
• If a function is untyped, it won't be checked
• If a function is typed, it will be checked for type errors
• If a function is partially typed, it will raise an error
• Dependencies aren't checked - only our code

As we develop or refactor stuff we can rework functions to have more type hints bit by bit. We can configure mypy to be stricter later on.

I also added a pre-commit configuration if that's your cup of tea 🍵

[codecov]

Codecov Report

Attention: Patch coverage is 93.75000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.51%. Comparing base (d5dd802) to head (1b15510).
Report is 1 commits behind head on fix-nonadditive.

Files with missing lines	Patch %	Lines
pgscatalog.core/src/pgscatalog/core/lib/models.py	93.54%	2 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##           fix-nonadditive      #50      +/-   ##
===================================================
+ Coverage            89.43%   89.51%   +0.08%     
===================================================
  Files                   38       38              
  Lines                 2347     2347              
===================================================
+ Hits                  2099     2101       +2     
+ Misses                 248      246       -2     

Flag	Coverage Δ
pgscatalog.core	90.75% <93.75%> (+0.15%)	⬆️

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