[WIP] Oxidize qubit tracker for HighLevelSynthesis

[alexanderivrii]

Summary

In #12911, we have added the QubitTracker class, which tracks the state of qubits for high-level synthesis. When HighLevelSynthesis runs non-trivially (i.e. does not take the "fast path", see #13070), this state tracking requires a large number of ssllllooooww Python set-based manipulations.

As an example, the following code

nq = 1000
qubits = tuple(range(nq))
qt = QubitTracker(qubits, set(qubits), set())
for i in range(nq // 2):
    for j in range(nq // 2):
        qt.used([i, j])

runs in about 3.2 seconds (on my laptop). The current PR almost verbatim reimplements QubitTracker in Rust, with the example above now running in 0.11 seconds (i.e. about 30x faster).

It also adds a few Python tests for QubitTracker.

This does not require release notes since QubitTracker is an internal class and should not be exposed to the users.

This is still work-in-progress because I would like to further revise QubitTracker's API and improve the internal data structures.

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Qiskit/terra-core
• @kevinhartman
• @mtreinish

[coveralls]

Pull Request Test Coverage Report for Build 10922540254

Details

• 124 of 161 (77.02%) changed or added relevant lines in 4 files are covered.
• 14 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.5%) to 88.804%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/accelerate/src/qubit_tracker.rs	121	158	76.58%

Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	1	92.98%
crates/accelerate/src/two_qubit_decompose.rs	1	91.45%
crates/qasm2/src/parse.rs	12	97.15%

Totals
Change from base Build 10919208944:	0.5%
Covered Lines:	73548
Relevant Lines:	82821

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💛 - Coveralls

[mtreinish]

I think a simple optimization you can make here is to use num_qubits: u32 instead of a Vec. In rust the Qubit object is just an integer in 0..n so it'll always be contiguous so we don't need to store the entire list and can just store the max index and then either do a comparison if it's in the circuit or an iterator (0..self.num_qubits) depending on how you were using qubits here.