WIP: Refactor the low-level interfaces

[fingolfin]

We can do some things more efficiently in OSCAR if we work with somewhat higher level in- and outputs

[codecov]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 77.83%. Comparing base (1085195) to head (64efeb1).
⚠️ Report is 25 commits behind head on master.

Files with missing lines	Patch %	Lines
gap/pari.gi	88.88%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #38   +/-   ##
=======================================
  Coverage   77.83%   77.83%           
=======================================
  Files          19       19           
  Lines        1561     1561           
=======================================
  Hits         1215     1215           
  Misses        346      346           

Files with missing lines	Coverage Δ
gap/field.gi	87.23% <100.00%> (+0.07%)	⬆️
gap/pari.gi	97.00% <88.88%> (-0.85%)	⬇️

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[fingolfin]

Right now this just shifted code around (and even duplicated it, once for OSCAR and once for PARI). The real idea here is that instead of asking OSCAR for coordinates in one basis and then we convert it here, instead we can directly get the desired coords from OSCAR.

But I've not yet done it.