Run all tests in wasm except for credentials tests

[ianthomas23]

This PR ensures that all tests are run in WebAssembly except for the credentials tests, support for which will follow in another PR.

Summary of changes:

1. Add the 4 test files not already covered (diff, fetch, push and tag).
2. Add monkeypatched functions os.rename, os.symlink and Path.write_bytes.
3. Rearrange the monkeypatched functions to satisfy linter.
4. New test function strip_ansi_colours which removes ANSI colour sequences from a string. This is needed because by default the normal linux/macos tests do not include colour sequences but the wasm ones do, so tests that check the contents of stdout returned by git2cpp functions need to remove colour sequences that are added. In future I am intending that we have some tests with and some without colour sequences for both the normal and wasm tests.
5. Remove passing env in subprocess.run as the commit_env_config fixture does this automatically.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.23%. Comparing base (1ed7644) to head (bbf967b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #123   +/-   ##
=======================================
  Coverage   88.23%   88.23%           
=======================================
  Files          60       60           
  Lines        2619     2619           
  Branches      309      309           
=======================================
  Hits         2311     2311           
  Misses        308      308           

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[ianthomas23]

Results of manual WebAssembly test run:

================== 249 passed, 9 skipped in 435.51s (0:07:15) ==================