Add resource tracking to NullQubit

[jzaia18]

Context:
For benchmarking, we need a method of precise resource tracking. This method has to be compatible with code run directly from PennyLane and should be able to track precise resources after various transformation passes have already occurred.

See also: https://github.com/PennyLaneAI/pennylane-benchmarks/pull/76 and PennyLaneAI/pennylane#7226

Description of the Change:
Adds 2 new class attributes to NullQubit, as well as an optional argument to its constructor. When this option is toggled on, NullQubit will track precise gate counts while "executing" a circuit and save them to a file when all qubits are released.

Benefits:
It is now possible to track precise gate counts (with or without gate decomposition or other transformation passes) for measuring circuit complexity.

Possible Drawbacks:
This implementation currently write the resources JSON to a file on disk as opposed to neatly returning an object back through to the Python caller in PennyLane. In the future, a more robust solution may be desired.

Related GitHub Issues:
[sc-91366]

[codecov]

Codecov Report

Attention: Patch coverage is 97.72727% with 3 lines in your changes missing coverage. Please review.

Project coverage is 96.65%. Comparing base (a2e4742) to head (c69b8f2).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
runtime/lib/backend/null_qubit/NullQubit.hpp	95.38%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1619      +/-   ##
==========================================
+ Coverage   96.53%   96.65%   +0.11%     
==========================================
  Files          82       82              
  Lines        9039     9170     +131     
  Branches      864      864              
==========================================
+ Hits         8726     8863     +137     
+ Misses        256      250       -6     
  Partials       57       57              

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[dime10]

Oh wow, I was just starting on this as well a couple of hours ago (just as a hack) 😆 Super useful though, thanks!

[maliasadi]

Thanks @jzaia18!

[dime10]

🎉

[maliasadi]

Nice work @jzaia18! 🥳 Just a few minor comments to resolve before merge!

[maliasadi]

Nice work @jzaia18! Just a few minor comments to consider before merging the PR.