add an option for full install,

[phlptp]

include impl headers with precompiled option.

This may be necessary for some package installs if they wish to include the precompiled static library alongside the header only install. inspired by #1198

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (e4ee3af) to head (21710ea).
⚠️ Report is 145 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##              main     #1252     +/-   ##
===========================================
  Coverage   100.00%   100.00%             
===========================================
  Files           17        19      +2     
  Lines         4546      5039    +493     
  Branches         0      1077   +1077     
===========================================
+ Hits          4546      5039    +493     

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