Use local copy of schema for autogen

[jmuhlich]

This avoids an unnecessary network access and speeds up autogen a lot.

[codecov-commenter]

Codecov Report

Merging #28 into master will decrease coverage by 0.26%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
- Coverage   95.20%   94.93%   -0.27%     
==========================================
  Files           1        1              
  Lines         396      415      +19     
==========================================
+ Hits          377      394      +17     
- Misses         19       21       +2     

Impacted Files	Coverage Δ
src/ome_autogen.py	94.93% <100.00%> (-0.27%)	⬇️

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