Optimize resource estimator pipeline

[austingmhuang]

Context:
The _update_counts_from_compressed_res_ops was doing brute force recursive tree traversal, which scales exponentially. As the recursive depth increases, this will lead to serious performance degradation.

Description of the Change:
We implement memoization to reduce the time complexity to polynomial.

Benefits:
Dramatic speed up of XAS notebook from 3 minutes to 4 seconds.

Possible Drawbacks:
None

Related GitHub Issues:

[codecov]

Codecov Report

❌ Patch coverage is 97.56098% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 99.44%. Comparing base (51e257d) to head (4be5b05).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
pennylane/estimator/estimate.py	97.56%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9021      +/-   ##
==========================================
- Coverage   99.44%   99.44%   -0.01%     
==========================================
  Files         601      601              
  Lines       64883    64917      +34     
==========================================
+ Hits        64523    64555      +32     
- Misses        360      362       +2     

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