other: include a rust-toolchain file

[ClementTsang]

Description

A description of the change, what it does, and why it was made. If relevant (such as any change that modifies the UI), please provide screenshots of the changes:

Issue

If applicable, what issue does this address?

Closes: #

Testing

If relevant, please state how this was tested. All changes must be tested to work:

If this is a code change, please also indicate which platforms were tested:

• Windows
• macOS
• Linux

Checklist

If relevant, ensure the following have been met:

• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, doc pages, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts
• If relevant, new tests were added (don't worry too much about coverage)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 40.61%. Comparing base (a794cc5) to head (6af4ec1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1503      +/-   ##
==========================================
- Coverage   40.63%   40.61%   -0.02%     
==========================================
  Files         103      103              
  Lines       17554    17554              
==========================================
- Hits         7133     7130       -3     
- Misses      10421    10424       +3     

Flag	Coverage Δ
macos-12	35.97% <ø> (ø)
ubuntu-latest	42.58% <ø> (-0.02%)	⬇️
windows-2019	36.13% <ø> (ø)

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