Add nambu projection to meanfield

[pablosanjose]

For MeanFields in Nambu space, it becomes necessary to impose the Nambu symmetries in order for the iteration solvers do not break said symmetries by accumulation of errors. This PR imposes said symmetries, that are different for rotated basis [c↑, c↓, c↓⁺, -c↑⁺] (meanfield keyword namburotation = true) or [c↑, c↓, c↑⁺, c↓⁺] (keyword namburotation = false). Default: false

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Codecov Report

Attention: Patch coverage is 43.24324% with 21 lines in your changes missing coverage. Please review.

Project coverage is 92.20%. Comparing base (53fbafc) to head (8701c31).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/meanfield.jl	41.66%	21 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #318      +/-   ##
==========================================
- Coverage   92.47%   92.20%   -0.27%     
==========================================
  Files          39       39              
  Lines        6906     6937      +31     
==========================================
+ Hits         6386     6396      +10     
- Misses        520      541      +21     

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[pablosanjose]

Closed in favor of #323