Optionally reuse flows for anti-commuting covers

[inmzhang]

This issue is found by one of my colleagues (Weiping Lin).

For the following circuit:

QUBIT_COORDS(0, 0) 0
QUBIT_COORDS(1, 0) 1
QUBIT_COORDS(2, 0) 2
R 0 1 2
TICK
CX 1 0
TICK
CX 1 2
TICK
MX 1
TICK
M 0 2

There should be two detectors DETECTOR rec[-1] and DETECTOR rec[-2]. However, annotate_detectors_automatically returns a single detector DETECTOR rec[-1] rec[-2]. This is because in

tqecd/src/tqecd/flow.py

Lines 90 to 93 in 7e47c39

	# Update the flows by removing the entries related to stabilizers that
	# will be merged and re-compute the anti-commuting stabilizers and map.
	for i in sorted(flows_indices_of_stabilizers_to_merge, reverse=True):
	flows.pop(i)

Every used flow is immediately removed and cannot be used anymore.

This PR adds an option to reuse the flows for further anticommuting cover opportunities. It's achieved by removing a single flow instead of all the flows each time. Note that it will significantly increase the runtime when this option is on but it enables more opportunities to find complete detectors.

[github-actions]

Package	Line Rate	Complexity	Health
src.tqecd	93%	0	✔
src.tqecd.match_utils	91%	0	✔
Summary	93% (787 / 847)	0	✔

[github-actions]

A preview of e50278f is uploaded and can be seen here:

✨ https://tqec.github.io/tqecd/pull/37/ ✨

Changes may take a few minutes to propagate.

[HaoTy]

Will try to review this PR over the weekend. Once we make the performance improvements to cover finding and the Pauli string, the overhead should be largely mitigated.