change "all" and "pdg" to be round modes instead of ndigits.

[jagerber48]

Addresses #185. Removes the "all" and "pdg" ndigits options and adds them as round_mode options.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (7fdb667) to head (773fb7a).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #188   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           24        24           
  Lines         1174      1171    -3     
=========================================
- Hits          1174      1171    -3     

Flag	Coverage Δ
3.10	100.00% <100.00%> (ø)
3.11	100.00% <100.00%> (ø)
3.12	100.00% <100.00%> (ø)
3.8	100.00% <100.00%> (ø)
3.9	100.00% <100.00%> (ø)
feature	93.90% <90.00%> (-0.02%)	⬇️
unit	63.91% <100.00%> (-0.10%)	⬇️

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