Add allow_non_hermitian parameter to BitArray.expectation_values (depends on #16443 partially fixes #11933)

[Yosef-Bunick]

Allow complex expectation values in BitArray.expectation_values
without a manual loop. Two flags unlock the path:
~ObservablesArray(obs, validate=False) > bypass Hermiticity gate
~expectation_values(obs, allow_non_hermitian=True) > complex return path

follow up to fix #16443
related to fix #11933 and fix #11393

AI/LLM disclosure

• I used the following tool to help write this PR description: ABE_v4 personal ai engine, All code reviewed, tested, and verified manually, with black formatting, 2 new tests, one for complex128 and one for float64

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[Yosef-Bunick]

PR #16488 opens the gate for array
moved to another pull since previous one is ready to go.
this one still needs tests review and addresses a different file, similar fix.

[Yosef-Bunick]

PR #16488 opens the gate but PR #16443 makes the engine work. #16488 without #16443 will return silent wrong answer. moved to another pull since previous one is ready to go but accidentally created pull with both in one file.

reopened with mutually independent separation between fixes.