[WIP] Proof of concept for using PyO3 in cargo unit tests.

[kevinhartman]

Summary

For now, this is mostly just a proof-of-concept. I'm making a non-draft PR to see how our CI setup works with this.

Details and comments

TBD.

[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 10912231140

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 28 of 30 (93.33%) changed or added relevant lines in 1 file are covered.
• 381 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.1%) to 88.81%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/circuit/src/dag_circuit.rs	28	30	93.33%

Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/expr.rs	1	94.02%
crates/qasm2/src/lex.rs	8	91.73%
crates/circuit/src/dag_circuit.rs	372	87.05%

Totals
Change from base Build 10892476121:	-0.1%
Covered Lines:	73467
Relevant Lines:	82724

---

💛 - Coveralls

[jakelishman]

If you enable the pyo3/auto-initialize feature during the test-suite build, then the pyo3::prepare_freethreaded_python calls won't be necessary. Don't know if you had other work around the test harness planned, though.