Read in capacity for parallel TreeMesh

[benegee]

Fixes restarting with AMR and MPI.
Resolves #1912

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.11%. Comparing base (76719a8) to head (9f27450).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1913   +/-   ##
=======================================
  Coverage   96.11%   96.11%           
=======================================
  Files         460      460           
  Lines       36926    36926           
=======================================
  Hits        35490    35490           
  Misses       1436     1436           

Flag	Coverage Δ
unittests	96.11% <100.00%> (ø)

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[ranocha]

Can we get a CI test for this, please?

[sloede]

Nice work! As commented by @ranocha, would it be possible to add a test for this as well?

[JoshuaLampert]

LGTM