Add NoDiscard attribute on mutation free methods

[Baptouuuu]

Since the attribute is not available on all supported versions Psalm complains. But this should be fine hence the error suppression in the config.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.78%. Comparing base (81a2b01) to head (8c796ea).

Additional details and impacted files

@@            Coverage Diff             @@
##             develop      #10   +/-   ##
==========================================
  Coverage      99.78%   99.78%           
  Complexity        58       58           
==========================================
  Files             16       16           
  Lines            920      920           
==========================================
  Hits             918      918           
  Misses             2        2           

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