Use `decomposition` instead of `Operator.expand`

[astralcai]

Operator.expand is deprecated (https://github.com/PennyLaneAI/pennylane/pull/5994). Operator.decomposition should be used instead.

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 80.99%. Comparing base (27813be) to head (c5e1dc2).

:exclamation: There is a different number of reports uploaded between BASE (27813be) and HEAD (c5e1dc2). Click for more details.

HEAD has 32 uploads less than BASE

| Flag | BASE (27813be) | HEAD (c5e1dc2) | |------|------|------| ||40|8|

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #846 +/- ## =========================================== - Coverage 98.40% 80.99% -17.42% =========================================== Files 113 17 -96 Lines 18413 1936 -16477 =========================================== - Hits 18120 1568 -16552 - Misses 293 368 +75 ```

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