Small speedup to construct DagDependency

[alexanderivrii]

Summary

Checking whether gates are over disjoint sets of qubits: if so, they commute, and the more expensive check using matrix multiplication is not necessary.

This is just a quick optimization. See also #8020.

Details and comments

A few experiments on random clifford circuits:

    gates = ["i", "x", "y", "z", "h", "s", "sdg", "cx", "cz", "swap"]
    qc = random_clifford_circuit(num_qubits, num_gates, gates=gates, seed=0)

#qubits = 5,  #gates =  100  : size = 100,  depth = 26,   #edges = 138,  previous time = 0.29,    new time = 0.07
#qubits = 5,  #gates =  500  : size = 500,  depth = 146,  #edges = 722,  previous time = 3.51,    new time = 1.49
#qubits = 5,  #gates =  1000 : size = 1000, depth = 294,  #edges = 1500, previous time = 11.41,   new time = 4.32
#qubits = 5,  #gates =  5000 : size = 5000, depth = 1478, #edges = 7144, previous time = 250.84,  new time = 95.89
#qubits = 10, #gates =  100  : size = 100,  depth = 13,   #edges = 131,  previous time = 0.40,    new time = 0.06
#qubits = 10, #gates =  500  : size = 500,  depth = 91,   #edges = 741,  previous time = 4.57,    new time = 0.87
#qubits = 10, #gates =  1000 : size = 1000, depth = 182,  #edges = 1535, previous time = 12.10,   new time = 2.77
#qubits = 10, #gates =  5000 : size = 5000, depth = 868,  #edges = 7358, previous time = 292.63,  new time = 64.49
#qubits = 20, #gates =  100  : size = 100,  depth = 9,    #edges = 100,  previous time = 0.49,    new time = 0.05
#qubits = 20, #gates =  500  : size = 500,  depth = 52,   #edges = 714,  previous time = 6.88,    new time = 0.83
#qubits = 20, #gates =  1000 : size = 1000, depth = 99,   #edges = 1564, previous time = 21.00,   new time = 2.67
#qubits = 20, #gates =  5000 : size = 5000, depth = 475,  #edges = 7617, previous time = 339.75,  new time = 55.36
#qubits = 50, #gates =  100  : size = 100,  depth = 4,    #edges = 55,   previous time = 0.56,    new time = 0.06
#qubits = 50, #gates =  500  : size = 500,  depth = 26,   #edges = 659,  previous time = 12.40,   new time = 1.01
#qubits = 50, #gates =  1000 : size = 1000, depth = 44,   #edges = 1464, previous time = 37.57,   new time = 2.77
#qubits = 50, #gates =  5000 : size = 5000, depth = 219,  #edges = 7741, previous time = 456.01,  new time = 50.24

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[coveralls]

Pull Request Test Coverage Report for Build 2341309331

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.005%) to 84.373%

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Totals
Change from base Build 2339583701:	0.005%
Covered Lines:	54530
Relevant Lines:	64630

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💛 - Coveralls

[kdk]

Changes and speed-ups look good to me.