Add .d_input()/.d_output() methods to Linear

[crutcher]

Pull Request Template

Checklist

• Confirmed that run-checks all script has been executed.
• Made sure the book is up to date with changes in this PR.

Changes

Added in/out introspection methods to Linear;
so assertions can be written relative to Linear's configs,
rather than reaching into the .weights.dim()[] manually.

Testing

Wrote a test.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.13%. Comparing base (26269a6) to head (d1028cc).
Report is 14 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2929   +/-   ##
=======================================
  Coverage   82.13%   82.13%           
=======================================
  Files         866      866           
  Lines      120052   120071   +19     
=======================================
+ Hits        98603    98619   +16     
- Misses      21449    21452    +3     

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[laggui]

Closing this for now following our previous discussion on discord 🙂