Allow users to add a custom API route

[aliabid94]

Now users can use gr.api to add custom API routes to their apps. For example:

    with gr.Blocks() as demo:
        def fn(a: int, b: int, c: list[str]) -> tuple[int, str]:
            return a + b, c[a:b]
        
        gr.api(fn, api_name="addition")

would add an API endpoint and API page that looks like this:

Note that it picks up type from type-hints. This endpoint will use the queue just like a normal endpoint.

It however does not yet pick up parameter and return type descriptions from the docstrings. This was because there's no consistent docstring format in python, especially for multiple return types - usually they are documented as a single return tuple which makes it hard to specify the indiviual types within the tuple. Can document in a follow up PR.

Closes: #10217

[gradio-pr-bot]

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---

Install Gradio from this PR

pip install https://gradio-pypi-previews.s3.amazonaws.com/bce06dd34658be9bf9f5cc66ed5001d003ae473c/gradio-5.11.0-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@bce06dd34658be9bf9f5cc66ed5001d003ae473c#subdirectory=client/python"

Install Gradio JS Client from this PR

npm install https://gradio-npm-previews.s3.amazonaws.com/bce06dd34658be9bf9f5cc66ed5001d003ae473c/gradio-client-1.9.0.tgz

Use Lite from this PR

<script type="module" src="https://gradio-lite-previews.s3.amazonaws.com/bce06dd34658be9bf9f5cc66ed5001d003ae473c/dist/lite.js""></script>

[gradio-pr-bot]

🦄 change detected

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Allow users to add a custom API route

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[abidlabs]

instead of setting the type to "state" which could have repercussions for other code, perhaps better to have a list of non-rendered components and include both "state" and "api"

[abidlabs]

It however does not yet pick up parameter and return type descriptions from the docstrings. This was because there's no consistent docstring format in python, especially for multiple return types - usually they are documented as a single return tuple which makes it hard to specify the indiviual types within the tuple. Can document in a follow up PR.

In that case, perhaps better to add explicit parameters parameter_descriptions and return_type_descriptions, but agreed this can be a separate pr. Could also add support for example_inputs which are currently missing in the view api page

[abidlabs]

Great PR @aliabid94! Generally works great. Just two suggestions:

1. Have a better error (or graceful fallback) if some of the type-hint is not specified. E.g. if you do this:

  def fn2(a: int, b: int, c):
      return a + b, c[a:b]
  
  gr.api(fn2, api_name="addition2")

the gradio app fails to launch with a messy error

2. (suggestion) use gr.api inside of gr.ChatInterface as a further test of robustness.

[aliabid94]

suggestion) use gr.api inside of gr.ChatInterface as a further test of robustness

Will do in a followup that also allows editing API description