feat: add Server-Sent Events (SSE) support

[BAIXIONGSODA]

PR: feat: add Server-Sent Events (SSE) support

Summary

Add support for Server-Sent Events (SSE) / EventStream in Chrome DevTools Network panel.

Problem

Previously, SSE responses (content-type: text/event-stream) were not properly displayed in DevTools because:

1. response.clone().arrayBuffer() waits for the entire stream to end before returning data
2. For long-running SSE connections (like AI chat completions), the stream never ends, so no data is shown
3. Even after stream ends, only the final combined data is shown without individual events

Solution

• Detect SSE responses by checking text/event-stream content-type
• Use ReadableStream to read chunks incrementally
• Parse SSE events (data, event, id fields) according to the SSE specification
• Send each event via Network.eventSourceMessageReceived CDP protocol
• Mark SSE responses as EventSource type in the Network panel

Changes

• packages/network-debugger/src/core/fetch.ts: Add SSE stream handling
• packages/network-debugger/src/fork/module/network/index.ts: Add eventSourceMessage handler
• Added comprehensive tests for SSE functionality
• Added SSE example endpoint in koa-esm demo

Testing

All 841 tests pass including new SSE-specific tests.

[GrinZero]

😊Thanks for your PR, I'll take a look over the weekend or on Friday

[GrinZero]

It's great, it looks like it's done to the basics mvp.

[GrinZero]

If you have time, you can improve it later:

1. Evenstream tab seems to have nothing
2. No way to know where the request was made?