ZQS-770 Make natural_key_revlex a default

[dexter2206]

This makes natural_key_revlex a default key for sorting symbols in ansatz.

As a reminder, using the aforementioned key results in the following order (assuming ansatz has symbols alpha_i, beta_j:
alpha_0 < beta_0 < alpha_1 < beta_1 < alpha_2 < beta_2 < alpha_3 < beta_3 < ....

[codecov]

Codecov Report

Merging #427 (4287694) into dev (d285f7f) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #427      +/-   ##
==========================================
- Coverage   90.94%   90.91%   -0.03%     
==========================================
  Files          63       63              
  Lines        3577     3577              
  Branches      575      575              
==========================================
- Hits         3253     3252       -1     
  Misses        217      217              
- Partials      107      108       +1     

Impacted Files	Coverage Δ
src/python/zquantum/core/interfaces/ansatz.py	75.00% <100.00%> (ø)
src/python/zquantum/core/openfermion/_utils.py	91.16% <0.00%> (-0.36%)	⬇️

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