Opt contraction

[ziofil]

Context:
At the moment a user has to figure out the optimal path to contract a circuit. This PR introduces a utility that computes the optimal path automatically and allows for custom heuristics.

Description of the Change:

Benefits:

Possible Drawbacks:

Related GitHub Issues:

[codecov]

Codecov Report

Attention: Patch coverage is 17.10037% with 223 lines in your changes are missing coverage. Please review.

Project coverage is 84.41%. Comparing base (680bf64) to head (808eff0).
Report is 2 commits behind head on develop.

❗ Current head 808eff0 differs from pull request most recent head a37cae6

Please upload reports for the commit a37cae6 to get more accurate results.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #397      +/-   ##
===========================================
- Coverage    87.44%   84.41%   -3.04%     
===========================================
  Files           81       82       +1     
  Lines         6142     6403     +261     
===========================================
+ Hits          5371     5405      +34     
- Misses         771      998     +227     

Files	Coverage Δ
mrmustard/lab_dev/circuit_components.py	96.13% <100.00%> (ø)
mrmustard/lab_dev/circuits.py	76.78% <18.51%> (-18.67%)	⬇️
mrmustard/lab_dev/opt_contraction.py	15.18% <15.18%> (ø)

... and 2 files with indirect coverage changes

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[SamFerracin]

delete this file?

[ziofil]

yep!