The FMP frame-boundary reader lived in transport/tcp/stream.rs, but the
Tor and Nym transports both reached across module boundaries to
'use crate::transport::tcp::stream::read_fmp_packet', a layering smell:
the reader is a shared stream-framing utility, not a TCP-private one.
Move the file to transport/framing.rs and repoint the tcp/tor/nym use
sites, removing the tor->tcp and nym->tcp dependencies. Behavior
unchanged.