Implement process_counts in ExpectationMP, VarianceMP and CountsMP

[Tarun-Kumar07]

Context:
Under #4941 abstract method process_counts was added to SampleMeasurement. This method provides support to process counts dictionary produced by external systems.

Description of the Change:

• Implement process_counts in ExpectationMP, VarianceMP and CountsMP.
• While implementing process_counts in CountsMP some common logic was extracted from ProbabilityMP to CountsMP

Benefits:
The below methods won't throw NotImplementedError exception

• ExpectationMP.process_counts
• VarianceMP.process_counts
• CountsMP.process_counts

Possible Drawbacks:

• All classes which inherit from SampleMeasurement implement process_counts except SampleMP.
  Should I add an implementation for that ?
• After implementing process_counts in all child classes can we make the method abstract similar to process_samples ? This might break some tests where some classes inherit from SampleMeasurement as there process_counts is not implemented
• It is assumed that counts dictionary is valid and caller is responsible to call with valid dictionary. It has already been discussed in this conversation and this is a design choice.

Related GitHub Issues:
This PR

• fixes Implement CountsMP.process_counts #5249
• fixes Implement VarianceMP.process_counts #5244
• fixes Implement ExpectationMP.process_counts #5241

---

Further details
I'm excited to be making my first open-source contribution with this PR 😄 .
As a newcomer to the community, I'm eager to learn and improve.
Any feedback for enhancements would be greatly appreciated!

Internal Shortcut Stories

• [sc-57166]
• [sc-57274]
• [sc-57307]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.63%. Comparing base (9d54b1c) to head (92fc70f).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5256      +/-   ##
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- Coverage   99.64%   99.63%   -0.01%     
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  Files         401      401              
  Lines       37215    36963     -252     
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- Hits        37082    36829     -253     
- Misses        133      134       +1     

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[Tarun-Kumar07]

I am not sure how to fix failing CI check, Can the reviewers please guide me?

[trbromley]

Thanks a lot for opening this @Tarun-Kumar07! We'll give this a review soon and also help with the CI issue you mentioned. Sorry if things are a little delayed this week, we're busy preparing for the PennyLane 0.35 release next week 🚀

[Tarun-Kumar07]

@trbromley Thank you for your response.
If there's anything I can do to help with the PennyLane 0.35 release preparations, please let me know.
I'd be more than happy to assist in any way I can! 🚀

[timmysilv]

hi @Tarun-Kumar07 , thanks for bearing with us! I've pushed a fix for the strange "Documentation Check" issue to the master branch. If you update your fork with the latest master, it should disappear 🤞 give it a try, I'll keep an eye out to make sure it's resolved here.

[Tarun-Kumar07]

@timmysilv all CI checks passed 🎉 , thanks for the fix.
This PR is now ready for review.

[albi3ro]

Sorry about the delay in review.

This is looking really great @Tarun-Kumar07 :)

I only have two main requests:

1. stripping out zeros entries if all_outcomes=False
2. Using qml.QueuingManager.stop_recording() around any location that creates an intermediary measurement process

But once those are done, I'll be happy to approve.

[Tarun-Kumar07]

Hey @albi3ro,

I noticed that all classes which inherit from SampleMeasurement implement process_counts except SampleMP. Should I add an implementation for that?

[albi3ro]

Just left a request to change the changelog entry to reference this PR, rather than the issues.

Looking great to me 🎉

Yes, we could also use SampleMP.process_counts, but we could potentially stick that into an independent PR instead.

[Tarun-Kumar07]

Hi @albi3ro and @trbromley,

Thanks for reviewing my PR.
It's my first open-source contribution, and I'm eager to contribute even more 🎉.

Appreciate it!

[Tarun-Kumar07]

@albi3ro, regarding adding SampleMP.process_counts.
Should I create a PR directly or make an issue about it?
What's the preferred process?

[astralcai]

Looks Good! 🎸

[albi3ro]

@albi3ro, regarding adding SampleMP.process_counts. Should I create a PR directly or make an issue about it? What's the preferred process?

I'll go ahead and create an issue right now.

Since this PR now has two approvals 🎉 , I'll go ahead and enable auto-merge. Congrats on the PR!

[trbromley]

Thanks @Tarun-Kumar07! Great job with this PR.

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