fix: deepcopy grammar constraint domains

[ReubenJ]

There is no related issue.

This fix is necessary to prevent subsequent constraints from modifying the previous constraints' domains.

Checklist

• I am following the contributing guidelines
• Tests are passing
• Lint workflow is passing
• Docs were updated and workflow is passing

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.70%. Comparing base (cac9500) to head (11ec2e6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #35      +/-   ##
==========================================
+ Coverage   97.05%   97.70%   +0.64%     
==========================================
  Files           2        2              
  Lines         136      174      +38     
==========================================
+ Hits          132      170      +38     
  Misses          4        4              

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