Install requirements.txt for mypy if present

[eirikurj]

Purpose

The current environment that mypy runs in does may not have the dependencies needed, e.g., numpy, mpi4py etc.

Instead, running mypy in our containers, or installing large number of python packages, we leave this up to the user and just check if there is a requirements.txt present in the repository and pip install that.

Note that this is the same PR as #23 as previously merged into dev. Also #25 needs to be merged first for the branch checks to pass.

Expected time until merged

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

Checklist

• I have run ruff check and ruff format to make sure the Python code adheres to PEP-8 and is consistently formatted
• I have formatted the Fortran code with fprettify or C/C++ code with clang-format as applicable
• I have run unit and regression tests which pass locally with my changes
• I have added new tests that prove my fix is effective or that my feature works
• I have added necessary documentation