Add helper to generate tty control sequence characters

Sending e.g. ctrl+c through a socket as `b'\x03'` isn't intuitive to read. We should include some nice enum/abstraction to generate these sequences.

The issue names no file, test, or entry point; begin by locating the socket-facing terminal/control-sequence code and existing public helper conventions. Clarify which control sequences the abstraction must cover, then add focused coverage showing that the ctrl+c example produces b'\x03' and that the public API is readable.

Written by the indexing model from the issue text.