Draft: Add support for Clifford+T target with NWQEC

[bachase]

First exploration of work towards #596.

For now this just adds two new passes that wrap the NWQEC compiler clifford compilation methods. Opening for any initial feedback, but before committing, will want to exercise this in the context of a broader fault-tolerant compilation workflow to see that this interface helps.

Some initial hesitations with the approach here:

1. This is implemented as a custom pass, which is the primary way to customize UCC functionality. However, these passes also transform the gateset, so interacts oddly with the target_gateset option to UCC overall.
2. NWQEC also has some pauli-based circuit optimizations, but uses a custom QASM dialect to represent them, so they won't translate back to Qiskit/QASM/Cirq or other representations.
3. I don't think theto_clifford_t/CliffordTPass do any specific optimization. Custom passes currently all happen at the end of the transpilation pipeline. If we want to optimize these in a customizable way, we might need to revisit the way users can specify passes.
4. The to_clifford_reduction/CliffordReductionPass does some clifford optimizations, but doesn't guarantee the circuit remains clifford+T? Or at least, I saw some pi/4 rotations in there that make it harder to asses.

[bachase]

@dobbse42 on this work in progress. As mentioned above, I think testing this against a specific use case will lead to a better design.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.94%. Comparing base (1b4212a) to head (bf13f11).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #597      +/-   ##
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+ Coverage   85.35%   86.94%   +1.58%     
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  Files           9       10       +1     
  Lines         280      314      +34     
  Branches       35       35              
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+ Hits          239      273      +34     
  Misses         29       29              
  Partials       12       12              

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[dobbse42]

@dobbse42 on this work in progress. As mentioned above, I think testing this against a specific use case will lead to a better design.

Thanks for the quick implementation! I'll go ahead and write a ucc layer in ftcc which uses this for Clifford+T transpilation prior to FT compilation, as this is at least my intended use case. Will tag it here once it's done.