fix: remove socket listeners on close to prevent memory leaks

[Stanzilla]

Summary

This PR fixes a memory leak that occurs when using passthrough mode in Node.js 20+.

The Problem

When MockHttpSocket.passthrough() is called, event listeners are attached to the original socket (lookup, connect, secureConnect, secure, session, ready, drain, data, error, resume, timeout, prefinish, finish, close, end) but they are never removed when the socket closes.

This causes memory leaks in long-running processes, as reported in mswjs/msw#2537.

The Fix

Call socket.removeAllListeners() in the close event handler before emitting the close event to the MockHttpSocket. This ensures all listeners attached to the original socket are properly cleaned up.

.on('close', (hadError) => {
  // Remove all listeners from the original socket to prevent memory leaks.
  // @see https://github.com/mswjs/msw/issues/2537
  socket.removeAllListeners()
  this.emit('close', hadError)
})

Test

Added a regression test that makes many passthrough requests and verifies no MaxListenersExceededWarning is emitted.

Fixes mswjs/msw#2537