file transfer server

[jiin-kim109]

Description:
https://docs.google.com/presentation/d/1Qct7UxwvBhyKCxd5ea97v5wHBfEuC2JSLGO9t8aCb8Y/edit?usp=sharing

Implement file transfer client module.

1. Create a thread and a socket for continuous communication until the file transfer ends.

2. a file server with ServerMode.Receiver should attempt to make connection to opponent file server with ServerMode.Sender. Then, the sender starts transmitting file based on the file info passed in init

Acceptance Criteria:

`
class FileServer:
def init(self, mode: ServerMode, file_info: File, ip_addr, port):
self.file_path = ""
pass

def send_file(self, receiver_ip_addr, receiver_port, chunk_start, chunk_end):
    if len(offsets) == 1:  # chunk end (exclusive)
        pass
    if len(offsets) == 2:  # chunk start, chunk end
        pass

def request_file(
    self, destination_filepath, sender_ip_addr, sender_port, chunk_start, chunk_end
):
    pass

`