Replace the type checking using property return_type with direct is…

[JerryChen97]

Context:
In the deprecations of PL0.41, the property return_type of class MeasurementProcess will be deprecated very soon PennyLaneAI/pennylane#6841. Therefore, we would like to replace the use of return_type with the equivalent direct isinstance check. For individual string info use of these return types, we replace them with in-place strings.

Description of the Change:
3 files are changed with equivalents in-place:

• pennylane_lightning/core/_adjoint_jacobian_base.py

• • Private staticmethod _get_return_type of class LightningBaseAdjointJacobian called return_type once, so replaced with equivalent isinstance
• • The private staticmethod _check_adjdiff_supported_measurements was only called by another private helper _process_jacobian_tape, therefore the two Enum type returns were replaced by strings, along with their conditional values in _process_jacobian_tape.
• • _process_jacobian_tape also called return_type once, therefore replace with equivalent isinstance.

• pennylane_lightning/core/lightning_base.py

• • The private staticmethod _check_adjdiff_supported_measurements was identified as not used by any code inside lightning. Therefore, we deleted it directly.

• tests/test_measurements.py

• • Two return_type usages were replaced with isinstance

Benefits:
Consistent with both v0.40 and v0.41 of PL

Possible Drawbacks:
Not aware of yet.

Related GitHub Issues:
[sc-71892]

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit .github/CHANGELOG.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 32.91%. Comparing base (24e429e) to head (34b1a1b).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pennylane_lightning/core/_adjoint_jacobian_base.py	14.28%	6 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (24e429e) and HEAD (34b1a1b). Click for more details.

HEAD has 40 uploads less than BASE

Flag	BASE (24e429e)	HEAD (34b1a1b)
	46	6

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1044       +/-   ##
===========================================
- Coverage   98.10%   32.91%   -65.20%     
===========================================
  Files         233       29      -204     
  Lines       39079     2634    -36445     
===========================================
- Hits        38339      867    -37472     
- Misses        740     1767     +1027     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[josephleekl]

Thanks @JerryChen97 ! Looks good, just have some quick questions before approving

[JerryChen97]

@maliasadi @AmintorDusko As described in description of change, the lines affected here are all in-line equivalents, therefore they should be no-effect towards any other files. However, codecov patch has been all the time 0 inside the changes of pennylane_lightning/core/_adjoint_jacobian_base.py, which I believe is caused by the fact that we actually do not have a direct unit test file for it; we should add another separate unit test file against this submodule in the future.

[AmintorDusko]

@JerryChen97, you might want to re-trigger the PR CIs with an empty commit.

[JerryChen97]

@AmintorDusko I removed ci build_wheels label and retriggered tests.

[AmintorDusko]

This is great! Thanks!