feat: first iteration of the purity data model and purity analysis

[lukarade]

Closes #5

Summary of Changes

Added the first iteration of the purity data model and the purity analysis. The analysis is capable of analyzing the purity of simple function definitions, as well as functions that interact with files.

Testing Instructions

run test_infer_purity

[lars-reimann]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	black	6	0	0	0.88s
✅ PYTHON	flake8	6		0	0.5s
✅ PYTHON	isort	6	0	0	0.27s
✅ PYTHON	mypy	6		0	2.37s
✅ PYTHON	pylint	6		0	5.32s
✅ REPOSITORY	git_diff	yes		no	0.04s

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[lars-reimann]

@lukarade I pushed a fix that should resolve some test failures.

[codecov]

Codecov Report

Merging #76 (38a06c8) into main (fd6a0f5) will increase coverage by 0.26%.
The diff coverage is 91.76%.

@@            Coverage Diff             @@
##             main      #76      +/-   ##
==========================================
+ Coverage   87.66%   87.92%   +0.26%     
==========================================
  Files          83       85       +2     
  Lines        3842     4107     +265     
==========================================
+ Hits         3368     3611     +243     
- Misses        474      496      +22     

Impacted Files	Coverage Δ
...c/library_analyzer/processing/api/model/_purity.py	88.76% <88.76%> (ø)
...c/library_analyzer/processing/api/_infer_purity.py	93.10% <93.10%> (ø)
src/library_analyzer/processing/api/__init__.py	100.00% <100.00%> (ø)
.../library_analyzer/processing/api/model/__init__.py	100.00% <100.00%> (ø)
src/library_analyzer/utils/_ASTWalker.py	97.22% <100.00%> (ø)

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[lukarade]

Like we discussed today, I want to close this PR, so it is easier to apply changes to the new branch without having to deal with merge conflicts afterwards. All requested changes will be applied on the new branch: https://github.com/Safe-DS/Library-Analyzer/tree/second-iteration-for-purity-analysis

[lars-reimann]

I want to close this PR

Do you want the PR to be merged or closed without being merged?