fix(application): FTP.make's args rejects bytearray/int with AttributeError instead of ProtocolError #2410

Describe the bug

FTP.make's args branch (pcapkit/protocols/application/ftp.py) accepts Optional[str | bytes], but anything that isn't bytes falls through to args.encode(...). A bytearray, int, bool, or memoryview raises a bare AttributeError instead of a ProtocolError.

PR #2365 widened the sibling cmmd parameter to also accept bytearray (for the same reason #2290 treats a bare AttributeError there as a defect), but left args as it was — the gap predates #2365 and isn't new to it.

To Reproduce

from pcapkit.protocols.application.ftp import FTP
FTP(cmmd='USER', args=bytearray(b'anonymous'))
# AttributeError: 'bytearray' object has no attribute 'encode'

args=42, args=True, and args=memoryview(b'x') fail the same way. str and bytes work correctly (no regression there); cmmd=bytearray already works since #2365.

Expected behavior

Accept (bytes, bytearray) directly and .encode() only a str; anything else raises ProtocolError naming the argument, matching cmmd's current guard.

Additional context

Found and verified during this session's #1103 prose sweep (not the sweep's own scope — flagged for a dedicated fix). Widen the type annotation and Raises: docstring, and add a test alongside the existing cmmd coverage.