Support variable depth in user defined ResourceOperations

[Jaybsoni]

Context:
PL now supports defining operations with custom resource requirements. Currently, tracking resources for operations with depth > 1 is not supported and yields a None value.

This PR adds support so that the depth is accurately computed for a workflow with custom operations.

Description of the Change:

• Update circuit graph and get_depth() method

[Jaybsoni]

[sc-37602]

[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

Merging #4033 (7ccbcff) into master (4c29082) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4033   +/-   ##
=======================================
  Coverage   99.72%   99.72%           
=======================================
  Files         351      351           
  Lines       30867    30903   +36     
=======================================
+ Hits        30783    30819   +36     
  Misses         84       84           

Impacted Files	Coverage Δ
pennylane/circuit_graph.py	100.00% <100.00%> (ø)
pennylane/resource/resource.py	100.00% <100.00%> (ø)
pennylane/tape/qscript.py	99.00% <100.00%> (+0.01%)	⬆️

[soranjh]

Thanks @Jaybsoni for adding this.

[DSGuala]

Looks good to me! Tried it for a few custom operations with random resources and it worked well.