Capture value and grad

[albi3ro]

Context:

We are trying to unify the pennylane and catalyst frontends into a single plxpr pipeline.

Description of the Change:

Adds a qml.value_and_grad function that works with both catalyst frontends.

Benefits:

Users can efficiently calculate the results and gradient at the same time.

Possible Drawbacks:

Related GitHub Issues:

[sc-106504]

[codecov]

Codecov Report

❌ Patch coverage is 89.24731% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.42%. Comparing base (240e2c5) to head (99f8f0d).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pennylane/_grad/value_and_grad.py	88.46%	9 Missing ⚠️
pennylane/tape/plxpr_conversion.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8814      +/-   ##
==========================================
- Coverage   99.44%   99.42%   -0.02%     
==========================================
  Files         601      602       +1     
  Lines       64894    64985      +91     
==========================================
+ Hits        64533    64613      +80     
- Misses        361      372      +11     

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