Bump version to 0.4.2

[drbenvincent]

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📚 Documentation preview 📚: https://causalpy--477.org.readthedocs.build/en/477/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.67%. Comparing base (4a1ad55) to head (cb66cbd).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #477   +/-   ##
=======================================
  Coverage   94.67%   94.67%           
=======================================
  Files          32       32           
  Lines        2196     2196           
=======================================
  Hits         2079     2079           
  Misses        117      117           

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