Added basic pyproject.toml.

[MichaelClerx]

• Closes Switch setup.py to pyproject.toml? #1692.
• Updates version no to 0.5.2 (should have happened earlier)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (79c05bd) to head (030762d).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1721   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           97        97           
  Lines         9701      9701           
=========================================
  Hits          9701      9701           

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[MichaelClerx]

Manually confirmed this fixes #1692