Make Flag[T] a pointer in prep for some future work

[FollowTheProcess]

• Make Flag a pointer type in prep for some future work
• Try out mise as a task runner

Summary

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.94%. Comparing base (eddca5d) to head (e59bb19).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/flag/set.go	25.00%	2 Missing and 1 partial ⚠️
internal/flag/flag.go	87.50%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #209      +/-   ##
==========================================
- Coverage   85.08%   84.94%   -0.14%     
==========================================
  Files           9        9              
  Lines        2085     2086       +1     
==========================================
- Hits         1774     1772       -2     
- Misses        243      245       +2     
- Partials       68       69       +1     

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