Fixes Wires objects as wire labels bug

[andrijapau]

Context:

Prior to this PR we had the following behaviour,

a = qml.wires.Wires("a")
b = qml.wires.Wires("b")
wires = [a,b,"c"]

>>> print(qml.wires.Wires(wires))
Wires([Wires(['a']), Wires(['b']), 'c'])

>>> print(qml.wires.Wires([0, 1, 2, 3, qml.wires.Wires([4, 5]), None]))
Wires([0, 1, 2, 3, Wires([4, 5]), None])

>>> print(qml.wires.Wires([qml.wires.Wires([(0,0), (0,1)])]))
Wires([Wires([(0, 0), (0, 1)])])

Description of the Change:

Add handling to _process that dissolves any Wires objects that survived to that point. This results in improved behaviour like,

a = qml.wires.Wires("a")
b = qml.wires.Wires("b")
wires = [a,b,"c"]

>>> print(qml.wires.Wires(wires))
Wires(['a', 'b', 'c'])

>>> print(qml.wires.Wires([0, 1, 2, 3, qml.wires.Wires([4, 5]), None]))
Wires([0, 1, 2, 3, 4, 5, None])

>>> print(qml.wires.Wires([qml.wires.Wires([(0,0), (0,1)])]))
Wires([(0, 0), (0, 1)])

Benefits:

Better visualization of wire objects.

Possible Drawbacks: Wire objects will look slightly different.

Related GitHub Issues: Fixes #6669

[sc-79749]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.59%. Comparing base (0ecf816) to head (446a27a).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6933   +/-   ##
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  Coverage   99.59%   99.59%           
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  Files         480      480           
  Lines       45505    45514    +9     
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+ Hits        45320    45329    +9     
  Misses        185      185           

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[JerryChen97]

Can we have in test suite the third example where tuples do not get flattened out ?

[JerryChen97]

The implementation looks good to me! Thanks for fixing this bug!

[PietropaoloFrisoni]

This looks flawless to me! 🥇

Only one question, maybe for @isaacdevlugt: since we are changing the wires visualization, should we mark this as a breaking change?