Convert to samples/counts based on available MPs

[lillian542]

Context:

In #1123 we changed the criteria for applying measurements_from_samples and measurements_from_counts to be based on whether or not there are supported observables. Previously the decision in preprocess had been based on supported measurement processes instead of supported observables. The reason for this change is that those transforms don't only change the measurement type - they also go a step further and diagonalize the observables to the readout basis. This is potentially a separate functionality from modifying measurement types.

There was discussion of this being handled by a future transform that is more specific to selectively transforming unsupported MPs without changing the observables. However, that isn't implemented yet, and the QRack plugin in analytic mode only supports Counts and Samples, so its needed now.

Description of the Change:
This PR reintroduces the check for supported measurement types being limited to a subset of {"Counts", "Samples"} in when adding measurement transforms to the device TransformProgram.

Benefits:
The QRack device keeps working.

Possible Drawbacks:
Depending what the backend supports, arguably the TOML file loading is what should change here - if the observables are only supported in analytic mode, then the qjit_capabilities in finite-shots mode should have an empty list of observables, and then this change would be unnecessary. So maybe I'm not fixing this in the most logical place? But I'm not sure about that, and I'm sure this will work.

[github-actions]

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[rmoyard]

Thanks for the quick change!

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.88%. Comparing base (621c027) to head (13dd59b).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
frontend/catalyst/device/qjit_device.py	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1148      +/-   ##
==========================================
- Coverage   97.89%   97.88%   -0.01%     
==========================================
  Files          76       76              
  Lines       10858    10863       +5     
  Branches     1281     1283       +2     
==========================================
+ Hits        10629    10633       +4     
  Misses        179      179              
- Partials       50       51       +1     

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[rmoyard]

Thanks for the quick fix 👍