add copy param to to_dask to avoid segfaults from closed file

[tlambert03]

No description provided.

[codecov-commenter]

Codecov Report

Merging #9 (fca8f2b) into main (bfdd429) will not change coverage.
The diff coverage is 0.00%.

@@          Coverage Diff          @@
##            main      #9   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files          8       8           
  Lines        862     863    +1     
=====================================
- Misses       862     863    +1     

Impacted Files	Coverage Δ
nd2/nd2file.py	0.00% <0.00%> (ø)

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