Bugfix for split_non_commuting when tape measurements is empty

[lillian542]

Context: Currently on master, if we apply split_non_commuting to a tape with empty measurements, we delete the tape:

>>> from pennylane.transforms import split_non_commuting
>>> tape = qml.tape.QuantumScript([qml.X(0)], measurements=[])
>>> tapes, _ = split_non_commuting(tape)
>>> tapes
[]

Description of the Change:

We add a check for len(measurements) == 0 and just return the tape if there are no measurements to split, so we get:

>>> from pennylane.transforms import split_non_commuting
>>> tape = qml.tape.QuantumScript([qml.X(0)], measurements=[])
>>> tapes, _ = split_non_commuting(tape)
>>> tapes
[<QuantumScript: wires=[0], params=0>]

Benefits: We don't delete the tape if it has no measurements (came up in catalyst tests)

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[codecov[bot]]

Codecov Report

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

Project coverage is 99.67%. Comparing base (fb06ce8) to head (2b569d0).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5869 +/- ## ========================================== - Coverage 99.68% 99.67% -0.01% ========================================== Files 421 421 Lines 40457 40165 -292 ========================================== - Hits 40328 40035 -293 - Misses 129 130 +1 ```

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[lillian542]

[sc-60186]

[lillian542]

Edit: wrong story ID [sc-60187]

[lillian542]

[sc-60188]