Test suite maintenance regarding qjit device capabilities

[paul0403]

One of the purposes of the QJITDevice class is to compute the preprocessing transform program depending on the device capabilities, i.e. what qnode-level transforms (aka qml.transfroms.blah) need to happen before reaching the mlir layer. For example, for devices without analytical mode execution, the measurement_from_samples/counts qnode transform is added here.

The code around here has recently been refactored https://github.com/PennyLaneAI/catalyst/pull/2089 (to account for whether the user has provided shots in the program, as well as just general clean up). One remaining function, get_device_capabilities , is not actually used in the codebase anymore. However, it was not deleted, because various tests are still using this internal function directly.

See https://github.com/PennyLaneAI/catalyst/pull/2089#discussion_r2421256201 for details.

The tests should properly construct custom capability sets for their respective purposes, instead of piggy-backing off lightning. As an alternative, the get_device_capabilities function can be demoted to a test util, and decoupled from the actual code base.