add n_dims parameter to Backend.__init__

[AgnieszkaZaba]

#1179

[AgnieszkaZaba]

@slayoo
Now we have the following error:

https://github.com/open-atmos/PySDM/actions/runs/37615388765/job/112776720241#step:4:2687

According to our change in #1885, we can't reuse environment instances for multiple particulators.

EDIT: II think we should change assert there

[AgnieszkaZaba]

So, it is interesting... I fixed this issue by reverting unintended change in the value of "n_dims". Previously in this test it was set to 0 (I set it to 2 because of the grid size).
I don't understand why it works now.

[codecov]

Codecov Report

❌ Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 87.46%. Comparing base (5853bd0) to head (74ec234).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
PySDM/exporters/vtk_exporter.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1964   +/-   ##
=======================================
  Coverage   87.46%   87.46%           
=======================================
  Files         429      429           
  Lines       11138    11140    +2     
=======================================
+ Hits         9742     9744    +2     
  Misses       1396     1396           

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[slayoo]

Kudos @AgnieszkaZaba !

Since this is aimed at closing #1179, we need to also remove the TODO label here:

PySDM/PySDM/environments/impl/register_environment.py

Line 9 in 5853bd0

for long execution times: see PR #1885""" # to be addressed in TODO #1179