add qml.math.grad and qml.math.jacobian for differentiating any interface

[albi3ro]

Context:

We often have to rewrite tests four different ways to test differentiability for each different interface. This is rather time-intensive and annoying. By adding and using a qml.math.grad, we can write one test that applies to all interfaces.

Description of the Change:

Adds a qml.math.grad and qml.math.jacobian with a jax-like interface that can differentiate with respect to any argument inputs.

Benefits:

Possible Drawbacks:

We have several different options for interface, but I decided to do my best to mirror the jax interface.

Related GitHub Issues:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.60%. Comparing base (b9df1e1) to head (e0fa72d).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6741   +/-   ##
=======================================
  Coverage   99.60%   99.60%           
=======================================
  Files         475      476    +1     
  Lines       45121    45210   +89     
=======================================
+ Hits        44944    45033   +89     
  Misses        177      177           

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[PietropaoloFrisoni]

🚀 🥳

[PietropaoloFrisoni]

Added a few suggestions to match the doc output on my laptop. Please let me know if it is different on yours 👍

[JerryChen97]

Looks all good on my side! Just several minor suggestions on error msg. Thanks a lot!

[JerryChen97]

Also, the similar error handling branch in grad.py seems missing tests coverage.

[PietropaoloFrisoni]

🚀