Add eventsource polyfill for Node.js and browser environments

[hannahblair]

Description

Replaces the Web API eventsource with eventsource to support Node.js environments. Also addresses window is not defined errors in Node.js.

To test, run the following in a node environment:

import { Client } from "@gradio/client";

const test = async () => {
    try {
	const app = await Client.connect("gradio/hello_world");
	const result = await app.predict("/predict", ["John"]);
	console.log("Result:", result);
    } catch (error) {
	console.error("Error:", error);
    }
};

(async () => {
	await test();
})();

Closes: #6352
Closes: #7103

🎯 PRs Should Target Issues

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Tests

1. PRs will only be merged if tests pass on CI. To run the tests locally, please set up your Gradio environment locally and run the tests: bash scripts/run_all_tests.sh

2. You may need to run the linters: bash scripts/format_backend.sh and bash scripts/format_frontend.sh

[gradio-pr-bot]

🪼 branch checks and previews

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---

Install Gradio from this PR

pip install https://gradio-builds.s3.amazonaws.com/d3c2e57646ef2bf9576c34cb7ed232ced11c00cf/gradio-4.28.3-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@d3c2e57646ef2bf9576c34cb7ed232ced11c00cf#subdirectory=client/python"

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
@gradio/client	patch
@gradio/upload	patch
gradio	patch

• Maintainers can select this checkbox to manually select packages to update.

With the following changelog entry.

Add eventsource polyfill for Node.js and browser environments

Maintainers or the PR author can modify the PR title to modify this entry.

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• If the bot has failed to detect any changes, or if this pull request needs to update multiple packages to different versions or requires a more comprehensive changelog entry, maintainers can update the changelog file directly.

[hannahblair]

@pngwn good thinking! i've added that now

i'm not sure if there's anything relevant that's checking for mode == "test" 🤔

[pngwn]

Small comment but looks great. Thanks for sorting this one out @hannahblair! This will be a huge boost to quality!

[pngwn]

Also closes #5840

I mean it closes this: ##5583

[pngwn]

Looks great! Thanks for ironing out the kinks with this one @hannahblair! And sorry for the back and forth!