feat: add langs field

[Uinelj]

1. Description

Adds the lang field on posts.

I haven't found any unit tests related to this, but do tell me if I need to add some somewhere :)

1.1. Checklist

• The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs: etc).
• I have read the Contributor Guide and followed the process outlined for submitting PRs.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples.

1.2. Breaking Change

• Yes, this is a breaking change.
• No, this is not a breaking change.

1.3. Related Issues

Fixes #640

[netlify]

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[github-actions]

Thanks for your contribution! :)

[codecov-commenter]

Codecov Report

Merging #642 (b64eff8) into main (40e16a4) will decrease coverage by 0.09%.
The diff coverage is n/a.

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@@            Coverage Diff             @@
##             main     #642      +/-   ##
==========================================
- Coverage   86.54%   86.46%   -0.09%     
==========================================
  Files         223      223              
  Lines        2475     2475              
==========================================
- Hits         2142     2140       -2     
- Misses        333      335       +2     

Files Changed	Coverage Δ
packages/bluesky/lib/src/entities/post_record.dart	100.00% <ø> (ø)

... and 1 file with indirect coverage changes

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[myConsciousness]

Hi @Uinelj !

There is a following unit test, but this is to ensure the minimum necessary behavior, so don't worry about it, at least not yet. I have already confirmed the correctness of your implementation. But well I plan to add more accurate tests in the future.

• https://github.com/myConsciousness/atproto.dart/blob/40e16a4c3f3a6c90c28e1fba66803f7baaf4a371/packages/bluesky/test/src/entities/adaptor/repo_commit_adaptor_test.dart

Thanks for your contribution, it looks good to me :)