misc: add __init__.py file to wgpu backend folder

[superlopuh]

A downstream client of xDSL currently can't import it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.27%. Comparing base (0d39a26) to head (016b922).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3731      +/-   ##
==========================================
- Coverage   91.28%   91.27%   -0.01%     
==========================================
  Files         468      467       -1     
  Lines       58601    58579      -22     
  Branches     5656     5656              
==========================================
- Hits        53492    53470      -22     
  Misses       3659     3659              
  Partials     1450     1450              

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[alexarice]

Is checking for these files precommitable/ci-able?

[superlopuh]

I don't know, I wonder if there's a setting we can disable somewhere to only allow imports from Python packages, it's not the first time this happens...