Add some typing

[dstansby]

Whilst I was trying to understand some of this code for cellfinder-napari purposes, I went through and added some typing. Hopefully this improves the documentation and makes some of the code clearer.

[codecov-commenter]

Codecov Report

Merging #18 (0473562) into master (0a2a6da) will decrease coverage by 0.62%.
The diff coverage is 26.92%.

@@            Coverage Diff             @@
##           master      #18      +/-   ##
==========================================
- Coverage   37.86%   37.24%   -0.63%     
==========================================
  Files          12       12              
  Lines         272      290      +18     
==========================================
+ Hits          103      108       +5     
- Misses        169      182      +13     

Impacted Files	Coverage Δ
brainglobe_napari_io/brainreg/reader_dir.py	0.00% <0.00%> (ø)
...be_napari_io/brainreg/reader_dir_standard_space.py	0.00% <0.00%> (ø)
brainglobe_napari_io/brainreg/utils.py	0.00% <0.00%> (ø)
brainglobe_napari_io/cellfinder/reader_dir.py	0.00% <0.00%> (ø)
brainglobe_napari_io/cellfinder/utils.py	88.09% <100.00%> (+1.60%)	⬆️

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[deprecated-napari-hub-preview-bot]

Preview page for your plugin is ready here:
https://preview.napari-hub.org/brainglobe/brainglobe-napari-io/18
Created: 2022-06-24T12:11:18.747133

[alessandrofelder]

Nice!