Add a transform to split sums to QJITDevice preprocess

[lillian542]

Context: Some backends do not natively support sums of observables (e.g. qml.expval(X(0) + Y(1))).

This is already taken care of by the split_non_commuting transform if the backend in question also doesn't support non-commuting observables, but applying split_non_commuting to handle sums on for devices that support non-commuting measurements will result in unnecessarily splitting executions into multiple tapes.

Description of the Change: If split_non_commuting is not being added to the transform program already, and the device does not support sum observables, we add the transform split_to_single_terms, which splits the sums but leaves them all on a single tape. Supporting either Hamiltonian or Sum is taken to indicate support for summed observables.

[lillian542]

[sc-60188] [sc-60187]

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Codecov Report

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

Project coverage is 97.92%. Comparing base (1e5c6d6) to head (3444494).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #927 +/- ## ======================================= Coverage 97.92% 97.92% ======================================= Files 71 71 Lines 10246 10255 +9 Branches 1162 1163 +1 ======================================= + Hits 10033 10042 +9 Misses 169 169 Partials 44 44 ```

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