How should devs contribute new transpiler passes? (WiP)

[jordandsullivan]

Based on the current architecture of UCC, we need to define a contribution guide for ourselves (and future contributors) for proposing, implementing, and validating a new technique.
My initial draft is as follows:

1. Proposing a new transpiler pass, including a report/template containing:
   a) How the technique works:
   i) In a written abstract without too much jargon, citing the source of the technique
   ii) (Optional, recommended): In a diagram showing an example circuit and how it would be affected by this pass
   b) Performance expectations:
   i) How much is the technique expected to reduce gate counts/compile time? (a rough estimate is okay, but this is how we prioritize which techniques to pursue, so we want to make a goodfaith effort to figure this out first)
   ii) Which types of circuits do we expect this technique to improve/ not improve?
   iii) Define test circuits of the above type which you will use to validate the technique.
2. Implementing and validating a protoype of the pass
   a) A jupyter notebook or small script is fine
   b) Validate using the circuits you defined in step 1.b.iii
3. Implementing the new pass in the codebase (can likely take inspiration from Qiskit: https://docs.quantum.ibm.com/guides/custom-transpiler-pass)
4. Clear acceptance criteria for being incorporated into UCCDefault1 (our default transpiler which runs when you call ucc.compile), e.g.
   a) reduction in compiled 2 qubit gate count
   b) reduction in runtime (for instance if the new technique replaces a slower one)
   c) How does this pass play with other passes? Does it perform as expected? (e.g. if a pass does well on its own, but not with the other existing passes)
   d) (Key metric) increase in "gate reduction factor per second" -- as defined in the UCC benchmarks notebook (screenshot below for reference)

Feel free to comment your suggestions below.

[jordandsullivan]

Full process should live in the Contribution Guide, the Proposal for New Transpiler Pass is part of New transpiler pass issue template.

[jordandsullivan]

@Misty-W can you note any changes to this guide based on the refactor #70 ?