Bun.$(...).lines() AsyncIterator does not stream

[ctjlewis]

What version of Bun is running?

1.1.41-canary.29+b8f28ed8a

What platform is your computer?

Darwin 24.1.0 arm64 arm

What steps can reproduce the bug?

Repro test: https://github.com/ctjlewis/bun-stream-lines (index.test.ts).

What is the expected behavior?

test("line iterator should iterate as lines are written to stream", async () => {
  const bunLines = 
    Bun
      .$`sleep 1; echo "1"; sleep 1; echo "2"; sleep 1; echo "3";`
      .lines()

  let lastTime = performance.now()
  for await (const line of bunLines) {
    const currentTime = performance.now()
    const delta = currentTime - lastTime

    console.log(`Line: ${line} took ${delta}ms`)
    lastTime = performance.now()
    
    expect(delta).toBeGreaterThan(1_000)
  }
})

The AsyncIterator returned by Bun.$(...).lines() should iterate as lines are written rather than being buffered. Had to revert to old Node APIs with callbacks, thought it was my bug.