Bugfix/mcm key dtype

[vincentmr]

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---

Context:
qml.counts does not return the same keys with dynamic_one_shot and defer_measurements.

Description of the Change:
Cast keys to the type produced by concretize.

Benefits:
Consistent keys.

Possible Drawbacks:
Slight (likely unnoticeable) performance decrease since NDArray object cannot be preallocated.

Related GitHub Issues:
#5566

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[dwierichs]

Thanks for the quick fix, @vincentmr
Could you add a test for the fix, maybe just the case from the issue? :)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (v0.36.0-rc0@b3c263f). Click here to learn what that means.

Additional details and impacted files

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[dwierichs]

Thanks @vincentmr !

[vincentmr]

[sc-61845]