Improve mcsolve performance

[albertomercurio]

Description

This PR improves the performance of mcsolve. This changes the way to compute which collapse operator is acting of the state. To do this, I preallocate the list of hermitian collapse operators $\hat{C}^\dagger \hat{C}$, making much easier to compute $\langle \psi \vert \hat{C}^\dagger \hat{C} \vert \psi \rangle$.

I already see some performance improvement in the benchmarks, and I expect more improvements when the initialization overhead is much less than the integration time.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.79%. Comparing base (110c2e5) to head (c6f9138).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #265      +/-   ##
==========================================
- Coverage   93.40%   92.79%   -0.61%     
==========================================
  Files          31       31              
  Lines        2334     2331       -3     
==========================================
- Hits         2180     2163      -17     
- Misses        154      168      +14     

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