Bugfixes: Simultaneous measurement of mutually commuting terms

[chmwzc]

The mapping of mutually generally commuting terms occasionally messes up the qubits to be measured if the given term group doesn't span the entire possible space, e.g.

from qibo.symbols import X, Y, Z
from qibo.hamiltonians import SymbolicHamiltonian

from qibochem.measurement.optimization import _gc_measurement_mapping

ham = SymbolicHamiltonian(X(2)*X(3) + Y(2)*Y(3) + Z(2)*Z(3), nqubits=4)
term_mapping, gates_to_add = _gc_measurement_mapping(ham.form, ham.nqubits, "chong")
print(f"{term_mapping = }")
# Output: term_mapping = {'X2 X3': Z1, 'Y2 Y3': -Z1*Z3, 'Z2 Z3': Z3} 
# Want: Qubits to be measured to remain as {2, 3}

This PR solves this by adding a dict to get back and use the original set of qubits after mapping the Pauli terms.

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Edit: Using this PR to fix some other bugs that JF found as well

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Edit 2: Reverting the addition of SWAP gates after circuit synthesis; it's simpler to just re-label instead. This PR is now just bug-fixing.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (89d00e1) to head (15e384b).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #196   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           13        13           
  Lines          990       996    +6     
=========================================
+ Hits           990       996    +6     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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