nodes: api fixes

[psychedelicious]

• 8693246 add image_to_dataURL util
• 0c26110 make fast latents method static
  • this method doesn't really need self and should be able to be called without instantiating Generator
• 2360bfb fix schema gen for GraphExecutionState
  • GraphExecutionState uses default_factory in its fields; the result is the OpenAPI schema marks those fields as optional, which propagates to the generated API client, which means we need a lot of unnecessary type guards to use this data type. the simple fix is to add config to explicitly say all class properties are required. looks this this will be resolved in a future pydantic release
• 3cd7319 fix step callback and fast latent generation on nodes. have this working in UI. depends on the small change in make step_callback work again in generate() call #2957

[damian0815]

lgtm