feature: support Prod as an observable

[ashlhans]

Issue #, if available:
#241

Description of changes:

Add support for Prod since Observables made with @ will now be instances of Prod instead of Tensor in the newest version of PennyLane (0.36.0)

Testing done:
tox and tox -e integ-tests

Merge Checklist

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Tests

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (3c7d620) to head (27962f6).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #244   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         7           
  Lines         1204      1207    +3     
  Branches       288       290    +2     
=========================================
+ Hits          1204      1207    +3     

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