Lazily dispatch grad and jacobian

[albi3ro]

Context:

When updating catalyst, I was getting extremely irritated by the fact that qml.qjit(qml.grad(f))(*args) does not work.

Description of the Change:

Lazily dispatch grad and jacobian so we can do qml.qjit(qml.grad(f)) and qml.qjit(qml.jacobian(f)).

Benefits:

Less rage. More intuitive experience.

Possible Drawbacks:

Related GitHub Issues:

[sc-100724]

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.42%. Comparing base (60f4f10) to head (10f9c03).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8382      +/-   ##
==========================================
- Coverage   99.42%   99.42%   -0.01%     
==========================================
  Files         584      584              
  Lines       61323    61338      +15     
==========================================
+ Hits        60972    60986      +14     
- Misses        351      352       +1     

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[dwierichs]

Just some tiny nitpick about the error message for non-qjit, and a question about performance in case of repeated execution.

[dwierichs]

Thanks, looks good to me 🎉