[bugfix] use resize_and_compute_masks in compute_masks

[psobolewskiPhD]

Closes #56

In this PR i replace using get_masks in compute_masks with resize_and_compute_masks. This results in minor additional refactor removing un-needed imports and function calls.

It appears to work correctly locally.

I will add a test once CI is fixed (#55)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 61.40%. Comparing base (ef6d108) to head (0d23ad4).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
cellpose_napari/_dock_widget.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #57      +/-   ##
==========================================
+ Coverage   54.31%   61.40%   +7.09%     
==========================================
  Files           3        3              
  Lines         232      228       -4     
==========================================
+ Hits          126      140      +14     
+ Misses        106       88      -18     

Flag	Coverage Δ
	61.40% <0.00%> (?)

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