Support kwargs predictors

[philandstuff]

This change allows a predictor input to be defined exclusively as **kwargs. This is an experimental change that allows a model to be used as a proxy where any inputs will be passed through directly without modification.

import json

def predict(**kwargs) -> str:
  return json.dumps(kwargs)

This change restricts the use of **kwargs to functions/methods that accept only that as an argument to avoid the complexity of having to support both dynamic and fixed inputs.

The OpenAPI schema for such a model will be:

{
   "properties": {},
   "additionalProperties": true,
   "type": "object",
   "title": "Input"
}

[aron]

@philandstuff I've reworked this PR to be a bit more restrictive. We now only allow models to use the **kwargs syntax as the sole argument. We also ignore the typing. This allows a model to receive arbitrary inputs but cog won't do any processing on these (such as downloading file inputs).

I think this is a good enough start for our use case.

[Copilot]

Pull Request Overview

This PR introduces experimental support for predictors that exclusively use **kwargs as input, enabling dynamic passthrough of input parameters for proxy models. Key changes include:

• Adding tests to verify kwargs input behavior.
• Implementing a new code branch in get_input_create_model_kwargs to support functions with only **kwargs.
• Updating the OpenAPI schema and adjusting create_model kwargs configuration.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
python/tests/server/test_http_input.py	Added test to validate dynamic kwargs inputs in predictions
python/tests/server/fixtures/input_kwargs.py	New predictor implementation accepting only **kwargs
python/cog/predictor.py	Updated input model generation logic to support exclusive **kwargs
.tool-versions	Updated Python version to 3.13.2

Comments suppressed due to low confidence (1)

python/tests/server/test_http_input.py:45

• [nitpick] The variable name 'input' shadows the built-in function. Consider renaming it to 'input_data' to improve clarity.

input = {"animal": "giraffe", "no": 5}

[Copilot]

[nitpick] Consider adding a comment explaining the purpose of the 'ExtraKeywordInput' class to clarify its role in handling exclusive **kwargs inputs.

[philandstuff]

@aron thanks for the polish. LGTM