Use Order[Version] to simplify MillAlg.content

[fthomas]

With our Version data type and its Order instance we can simplify MillAlg.content because we can just check if a Mill version is >= 0.7 and < 0.9 for example without extracting the minor version number.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.77%. Comparing base (26f9dd0) to head (5db3157).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3540      +/-   ##
==========================================
- Coverage   89.77%   89.77%   -0.01%     
==========================================
  Files         171      171              
  Lines        4979     4976       -3     
  Branches      496      492       -4     
==========================================
- Hits         4470     4467       -3     
  Misses        509      509              

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