Move conv autotune under feature flag (except key)

[laggui]

Checklist

• Confirmed that run-checks all script has been executed.

Related Issues/PRs

Stumbled upon this while validating the changes in #2311 with the mnist-inference-web example (using wgpu)

Changes

When autotune feature flag is not used, the autotune key should still be available otherwise its usage in JitAutotuneKey will throw some unresolved import errors.

Testing

Works with mnist-inference-web example on wgpu.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.37%. Comparing base (99d9fa2) to head (7819571).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2330   +/-   ##
=======================================
  Coverage   85.37%   85.37%           
=======================================
  Files         768      769    +1     
  Lines       98673    98673           
=======================================
  Hits        84238    84238           
  Misses      14435    14435           

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