[Capture] add eval_jaxpr method to null.qubit

[albi3ro]

Context:

I'm starting to some information about the pros and cons of program capture and how to use it.

I'd like to just demonstrate some basics about the classical overheads and scaling, and would like to use null.qubit to do so.

Description of the Change:

Adds an eval_jaxpr method to null.qubit.

Benefits:

We can examine the classical overheads associated with null.qubit.

Possible Drawbacks:

Related GitHub Issues:

[sc-83829]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.59%. Comparing base (53df3dc) to head (0cb55de).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6924   +/-   ##
=======================================
  Coverage   99.59%   99.59%           
=======================================
  Files         480      480           
  Lines       45496    45505    +9     
=======================================
+ Hits        45311    45320    +9     
  Misses        185      185           

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[mudit2812]

One comment, otherwise ready to approve.

[andrijapau]

LGTM! 🚀