将WritableStream的内容存储到Blob中。这可以通过将WritableStream转换为ReadableStream，然后将其转换为ArrayBuffer，最后将ArrayBuffer存储到Blob中来完成。

import { CAREncoderStream, createDirectoryEncoderStream } from 'ipfs-car'
import { WritableStream, ReadableStream } from 'node:stream/web'

export const packCAR = async (files) => {
  const blockStream = createDirectoryEncoderStream(files)
  const carEncoderStream = new CAREncoderStream([])
  const chunks = []
  const outStream = new WritableStream({
    write(chunk) {
      chunks.push(chunk)
    },
    close() {
      console.log('Stream is closed.')
    }
  })
  await blockStream.pipeThrough(carEncoderStream).pipeTo(outStream)
  const arrayBuffer = await new Blob(chunks).arrayBuffer()
  const blob = new Blob([arrayBuffer])
  return blob
}