Fix rrules for Fermionic symmetries

[qmortier]

rrules for tensorcontract etc for fermions

[codecov]

Codecov Report

Attention: Patch coverage is 96.29630% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 81.95%. Comparing base (4607691) to head (73992c9).

❗ Current head 73992c9 differs from pull request most recent head 39942c1

Please upload reports for the commit 39942c1 to get more accurate results.

Files	Patch %	Lines
src/tensors/adjoint.jl	0.00%	2 Missing ⚠️
src/tensors/indexmanipulations.jl	84.61%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #126      +/-   ##
==========================================
+ Coverage   81.44%   81.95%   +0.51%     
==========================================
  Files          42       42              
  Lines        5588     5680      +92     
==========================================
+ Hits         4551     4655     +104     
+ Misses       1037     1025      -12     

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[lkdvos]

I rebased this on the current master and added a few changes that simplify the implementations.

Most notably I added a method for twisting multiple tensor indices at the same time. I'll finish this up tomorrow, but I would like to add:

• some tests for the vectorized twist I realised later that this is already used in tensorcontract
• some simplifications in the tensortrace implementation

[Jutho]

I guess something is off with the random number generator on Julia 1.6 :-)

[lkdvos]

I am investigating now, but I have no clue what is going on here

[lkdvos]

So, as far as I can tell, the issue arises whenever the SVD is truncating between two singular values that are close together, such that the FiniteDifferences calls yield different sizes of tensors, which then ofcourse cannot be added.
I changed some of the parameters around, and hope that it works now, but it's definitely not "fixed".

[lkdvos]

Everything seems to turn green again, ready to go for me!

[Jutho]

I forgot to mention that the doc string needed an update to reflect the is argument here.