File operations

# 쓰기 (내용은 바이트여야 함)
sandbox.write_file("/tmp/hello.txt", b"Hello!").result()

# 읽기 (bytes 반환)
content = sandbox.read_file("/tmp/hello.txt").result()
print(content.decode())

refs = [sandbox.write_file(f"/tmp/{i}.txt", b"data") for i in range(5)]
for ref in refs:
    ref.result()