Improve pseudo inverse spectrum

[albertomercurio]

Checklist

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Description

I slightly improve the cache initialization of the pseudo inverse method of spectrum. This is also a test to see if the Benchmark Tracking still returns an error as in #386 .

Additional context

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.59%. Comparing base (0408069) to head (23f38ae).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #388   +/-   ##
=======================================
  Coverage   93.59%   93.59%           
=======================================
  Files          44       44           
  Lines        2826     2827    +1     
=======================================
+ Hits         2645     2646    +1     
  Misses        181      181           

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[albertomercurio]

Ok, the benchmarks passed. I don't know what happened.

[albertomercurio]

Also in the main