Fix dynamical fock dimension saving

[albertomercurio]

Checklist

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Description

The previous implementation was returning an error when using the saveat argument. This was caused by a wrong saving of the dims during the evolution.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.18%. Comparing base (d0f0b11) to head (dea7310).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #375   +/-   ##
=======================================
  Coverage   93.18%   93.18%           
=======================================
  Files          43       43           
  Lines        2788     2790    +2     
=======================================
+ Hits         2598     2600    +2     
  Misses        190      190           

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