merge api.nodes into api.schemas

[liamhuber]

Before a 1.0 release we'll need to look together and decide what the most sensible API is. In the meantime, it has felt weird to me that all the other classes and models are all in schemas but the nodes are off here by themselves. So just merge them in with the rest of the types.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.24%. Comparing base (c71e830) to head (a210936).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #194   +/-   ##
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  Coverage   99.24%   99.24%           
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  Files          33       33           
  Lines        2652     2652           
=======================================
  Hits         2632     2632           
  Misses         20       20           

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