Allow for Executor class and batched Executors for LRE

[bdg221]

Fixes #2668
Fixes #2675

This PR updates the LRE technique to allow for Executor class objects to be passed in to execute_with_lre. Along with that update, there is also an update to allow for a batched executor.

License

• I license this contribution under the terms of the GNU GPL, version 3 and grant Unitary Fund the right to provide additional permissions as described in section 7 of the GNU GPL, version 3.

Before opening the PR, please ensure you have completed the following where appropriate.

• I added unit tests for new code.
• I used type hints in function signatures.
• I used Google-style docstrings for functions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.74%. Comparing base (f404e28) to head (74b8641).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2676   +/-   ##
=======================================
  Coverage   98.74%   98.74%           
=======================================
  Files          93       93           
  Lines        4219     4223    +4     
=======================================
+ Hits         4166     4170    +4     
  Misses         53       53           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[natestemen]

Great work!

A suggestion for the tests: we should steer away from testing accuracy in the tests. This type of test often leads to non-deterministic behavior which causes spurious failures. I'd recommend two different tests instead:

1. Ensure the evaluate method has been called $n$ times on the Executor object when the executor cannot batch, and there are $n$ circuits to run.
2. Ensure the evaluate method is only called once when the executor can batch.

WDYT?

[natestemen]

I know this is the pattern we have in zne/zne.py, but I think it's more readable to have

if executor_obj.can_batch:
    ...
else:
    # cannot batch

[bdg221]

@natestemen I like your idea for the tests. Unfortunately, for testing mitigate_executor, we cannot check calls_to_executor because it does not have an accessible Executor object. The tests for that scenario use accuracy (ZNE, PEC, DDD). If we wanted to avoid accuracy for the mitigate_executor, the code would need to change across the techniques.