Use not mutable fields on Viewer where appropriate

[sofroniewn]

Description

Following the release of pydantic 1.8.x and pydantic/pydantic#2196 we can now use field not mutable fields where appropriate on our Viewer. This will prevent people from overwriting the dims, or trying to set things that cannot be set. We also won't add event emitters for these fields as they cannot be changed.

Technically this is a breaking change, but I'm not quite sure how anyone would have successfully set these things before!

It should be reviewed after we fix our CI with 1.8.1 (see #2322). Note this will bump our min pydantic requirement to 1.8.1 as allow_mutation=False was previously not supported.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

[tlambert03]

I like it! but is pydantic >1.8.1 required for this?

[sofroniewn]

I like it! but is pydantic >1.8.1 required for this?

Yes I'm pretty sure, the allow_mutation kwarg wasn't added until 1.8.0 see pydantic/pydantic#2196 so unless they backported it, it shouldn't work - but I havn't tried it!

[tlambert03]

eh, fine with me either way. since we're already >=1.7.3, I'm not sure that single version is all that important

[codecov]

Codecov Report

Merging #2346 (5faafb1) into master (5a2b3c3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2346   +/-   ##
=======================================
  Coverage   80.85%   80.86%           
=======================================
  Files         433      433           
  Lines       35724    35736   +12     
=======================================
+ Hits        28886    28898   +12     
  Misses       6838     6838           

Impacted Files	Coverage Δ
napari/components/_tests/test_viewer_model.py	100.00% <100.00%> (ø)
napari/components/viewer_model.py	94.24% <100.00%> (ø)
napari/utils/events/evented_model.py	96.47% <100.00%> (+0.17%)	⬆️

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[sofroniewn]

eh, fine with me either way. since we're already >=1.7.3, I'm not sure that single version is all that important

Ok nice, I will merge this now. I think we then have a fresh start with >= 1.8.1. Thanks!!