Add general Heisenberg Hamiltonian and XXX model

[renatomello]

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.68%. Comparing base (9e00ebd) to head (707a106).
Report is 17 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1538   +/-   ##
=======================================
  Coverage   99.68%   99.68%           
=======================================
  Files          80       80           
  Lines       11586    11606   +20     
=======================================
+ Hits        11550    11570   +20     
  Misses         36       36           

Flag	Coverage Δ
unittests	99.68% <100.00%> (+<0.01%)	⬆️

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[andrea-pasquale]

Thanks @renatomello, I've just a small suggestion.

[andrea-pasquale]

Perhaps we could drop this given that a similar check is performed in the Heiseinberg function.

qibo/src/qibo/hamiltonians/models.py

Lines 183 to 187 in 707a106

	if isinstance(coupling_constants, (list, tuple)) and len(coupling_constants) != 3:
	raise_error(
	ValueError,
	f"When `coupling_constants` is type `int` or `list`, it must have length == 3.",
	)