Allow a custom equals parameter for observable collections

[amondnet]

Describe the changes proposed in this Pull Request.

Allow a custom equals parameter for observable collections, like observable stream, observable and computed .

#771
#482

If the PR fixes a specific issue, reference the issue with Fixes #.

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Pull Request Checklist

• If the changes are being made to code, ensure the version in pubspec.yaml is updated.
• Increment the major/minor/patch/patch-count, depending on the complexity of change
• Add the necessary unit tests to ensure the coverage does not drop
• Update the Changelog to include all changes made in this PR, organized by version
• Run the melos run set_version command from the root directory
• Include the necessary reviewers for the PR
• Update the docs if there are any API changes or additions to functionality

[netlify]

👷 Deploy request for mobx pending review.

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🔨 Latest commit	d13d88d

[codecov]

Codecov Report

Merging #970 (d13d88d) into main (d14a27e) will decrease coverage by 0.62%.
Report is 3 commits behind head on main.
The diff coverage is 83.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #970      +/-   ##
==========================================
- Coverage   99.00%   98.38%   -0.62%     
==========================================
  Files          57       57              
  Lines        2005     2043      +38     
==========================================
+ Hits         1985     2010      +25     
- Misses         20       33      +13     

Flag	Coverage Δ
flutter_mobx	100.00% <ø> (ø)
mobx	97.69% <83.33%> (-0.88%)	⬇️
mobx_codegen	100.00% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...rc/api/observable_collections/observable_list.dart	99.20% <90.00%> (-0.80%)	⬇️
...src/api/observable_collections/observable_map.dart	98.41% <89.47%> (-1.59%)	⬇️
...src/api/observable_collections/observable_set.dart	91.17% <76.92%> (-8.83%)	⬇️

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