Use small chunks with toStream()

[huan]

Write a big chunk to stream will cause problems like block event loop

Especially here:

file-box/src/file-box.ts

Lines 492 to 495 in cf6caf5

	private transformBufferToStream (buffer?: Buffer): Readable {
	const bufferStream = new PassThrough()
	bufferStream.end(buffer || this.buffer)
	return bufferStream

Here's a solution: ChunkerTransformStream, a transform stream to take arbitrary chunk sizes and make them consistent

CC: @windmemory