Remove warnings from state plotter

[SamFerracin]

Context:

from mrmustard.lab import *
Vacuum(1)

Executing the code above triggers a long list of annoying warnings, displayed between the recap of the state and the phase-space plot.

Description of the Change:
This PR removes the cause of the warnings, without changing the way that the plot looks

[sylviemonet]

Tbh, I can not reproduce the same warnings on my dev container in the branch develop.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (429b16c) 84.14% compared to head (7a76be4) 84.14%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #343   +/-   ##
========================================
  Coverage    84.14%   84.14%           
========================================
  Files           65       65           
  Lines         4775     4775           
========================================
  Hits          4018     4018           
  Misses         757      757           

Files	Coverage Δ
mrmustard/lab/abstract/state.py	92.37% <100.00%> (ø)

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 429b16c...7a76be4. Read the comment docs.