Add TCP timeouts and bounded delimiter reads

[lukewilliamboswell]

Context

The TCP API currently has no way to bound connection, read, or write duration:

• TcpStream::connect is used directly in src/tcp.rs:171-184
• reads and writes have no socket deadlines
• tcp_read_until_impl grows a Vec until the delimiter or EOF at src/tcp.rs:92-115

A peer that never finishes connecting, never sends the requested bytes/delimiter, or continuously sends data without the delimiter can hang the program or grow memory without bound.

Suggested direction

Add deadline/timeout-aware variants for:

• connect;
• read;
• write.

Add a bounded delimiter operation such as read_until!(stream, delimiter, max_bytes), or make the existing operation accept a limit if the API can still change before stable.

Keep error mapping portable and distinguish timeout from EOF and size-limit exhaustion. Be careful that DNS resolution can also block and may need separate treatment from per-address connect_timeout.

Acceptance criteria

• A caller can bound TCP connection, read, and write time.
• Delimiter reads have a finite caller-selected or documented maximum size.
• Timeout, unexpected EOF, and size-limit errors are distinct.
• Tests use a local helper server to cover stalled connect/read behavior and an over-limit delimiter-free stream.
• Existing unbounded behavior is either retained under explicitly named APIs or documented as a compatibility choice.