Channel from XY

[arsalan-motamedi]

Context:
We would like to have the ability to initialize a Channel from its X,Y matrices (and potentially a d vector).

Description of the Change:
Added the method .from_XY which allows this computation.

Benefits:
Provides a simpler way for a user to initialize their desired channel.

Possible Drawbacks:
None.

Related GitHub Issues:
None.

[apchytr]

Some minor comments but looks great! Thanks!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.80%. Comparing base (e5c02ce) to head (517d6f5).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #514      +/-   ##
===========================================
+ Coverage    89.77%   89.80%   +0.03%     
===========================================
  Files           92       92              
  Lines         6054     6072      +18     
===========================================
+ Hits          5435     5453      +18     
  Misses         619      619              

Files with missing lines	Coverage Δ
mrmustard/lab_dev/transformations/base.py	99.42% <100.00%> (+0.01%)	⬆️
mrmustard/physics/triples.py	100.00% <100.00%> (ø)

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