Implement a minimal Fci functionality on master

[totork]

Purpose

Fci is currently running on a separate branch. This diverges signifcant effort of us into separate codes. This first PR aims to adjust Hermes-3 to use the Fci implementation of Bout++ that was updated recently.

Change Summary

Mostly changes hidden behind .isFci() - flags. It is mainly preserving parallel slices by using .asField3DParallel() at certain positions where its needed

Validation

Added 3 1-D MMS test (density, momentum & pressure) for Fci that pass, including the CI.

AI Assistance

Nope.

Documentation

Not yet

Review Notes

This branch is forked from

https://github.com/boutproject/hermes-3/tree/compile-3dmetric

so it certainly needs

#577

To do:

• Check the BOUT++ version

[codecov]

Codecov Report

❌ Patch coverage is 34.56376% with 195 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.56%. Comparing base (412b099) to head (9c07230).

Files with missing lines	Patch %	Lines
src/div_ops.cxx	34.12%	139 Missing ⚠️
src/evolve_pressure.cxx	28.57%	12 Missing and 3 partials ⚠️
src/evolve_momentum.cxx	42.10%	7 Missing and 4 partials ⚠️
include/fixed_velocity.hxx	25.00%	4 Missing and 2 partials ⚠️
include/fixed_temperature.hxx	16.66%	3 Missing and 2 partials ⚠️
include/fixed_density.hxx	0.00%	3 Missing and 1 partial ⚠️
src/evolve_density.cxx	33.33%	2 Missing and 2 partials ⚠️
src/recycling.cxx	55.55%	4 Missing ⚠️
src/diamagnetic_drift.cxx	0.00%	2 Missing ⚠️
src/electromagnetic.cxx	0.00%	2 Missing ⚠️
... and 3 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #629      +/-   ##
==========================================
+ Coverage   57.53%   57.56%   +0.02%     
==========================================
  Files          98       97       -1     
  Lines       10223    10078     -145     
  Branches     1466     1459       -7     
==========================================
- Hits         5882     5801      -81     
+ Misses       3753     3682      -71     
- Partials      588      595       +7     

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[dschwoerer]

@totork I did not intend to close this PR.

It somehow got closed while merging #577

Even worse, I cannot reopen it, as the target branch got merged and deleted. Normally that should move the PR to point towards the new branch, but for some reason, I cannot even update it to that. For some reason, it worked for #633 - but not for this one.