Transforms can be captured with PLxPR

[mudit2812]

[sc-72804] [sc-72803]

This PR adds a primitive for capturing transforms.

Description of change

• Add a primitive to capture transforms: every time a transform is created, it automatically gets registered as a primitive
• This primitive is currently only for capturing transforms and does not actually transform the input function.
• This primitive gets bound (binded?) when calling the transform on the QNode or a function.
  • When applied to a function, the transform is captured as a higher-order primitive. Evaluating the subsequent JAXPR doesn't do anything (i.e, the inner JAXPR is evaluated without any transformations)
  • When applied to a QNode, the transform is appended to the QNode's TransformProgram as well so that executing QNodes applies the transform(s) to the constructed tape, and also captured as a primitive.
• Add plxpr_transform attribute to TransformDispatcher and TransformContainer. This is not currently used and is being added here to set up scaffolding in pennylane.transfoms.core for Add TransformTrace, TransformTracer and TransformInterpreter classes for transforming PLxPR #6389 .

Benefits
Transforms can be captured into PLxPR and no extra work is required when creating new transforms

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.65%. Comparing base (343ecc1) to head (ce560d5).
Report is 2 commits behind head on master.

Additional details and impacted files

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##           master    #6633   +/-   ##
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  Coverage   99.65%   99.65%           
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  Files         459      459           
  Lines       43217    43262   +45     
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+ Hits        43068    43113   +45     
  Misses        149      149           

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[PietropaoloFrisoni]

Thanks, no blockers from me.

It seems to me that we are not systematically using type hints anymore, so I guess this should not be a requirement for new changes in the codebase

[albi3ro]

👍