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:
4 files are changed with equivalents in-place:

• pennylane_lightning/core/_adjoint_jacobian_base.py
• pennylane_lightning/core/_version.py
• pennylane_lightning/core/lightning_base.py
• tests/test_measurements.py

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 16.66667% with 10 lines in your changes missing coverage. Please review.

Project coverage is 27.36%. Comparing base (290c986) to head (8591013).

Files with missing lines	Patch %	Lines
pennylane_lightning/core/_adjoint_jacobian_base.py	14.28%	6 Missing ⚠️
pennylane_lightning/core/lightning_base.py	0.00%	4 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (290c986) and HEAD (8591013). Click for more details.

HEAD has 106 uploads less than BASE

Flag	BASE (290c986)	HEAD (8591013)
	112	6

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1044       +/-   ##
===========================================
- Coverage   98.10%   27.36%   -70.75%     
===========================================
  Files         233       29      -204     
  Lines       39079     2646    -36433     
===========================================
- Hits        38339      724    -37615     
- Misses        740     1922     +1182     

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