Add TCP timeouts and bounded delimiter reads

[lukewilliamboswell]

Summary

• require an explicit deadline on every TCP connect, read, and write operation
• apply connect deadlines across DNS resolution and every resolved address
• require delimiter and line reads to specify both a byte limit and a deadline
• distinguish timeout, unexpected EOF, and read-limit exhaustion errors
• add local TCP tests for stalled connects, stalled reads, EOF, and delimiter-free over-limit streams

API direction

This intentionally changes the primary API instead of retaining compatibility variants:

• Tcp.connect!(host, port, timeout_ms)
• stream.read_up_to!(bytes, timeout_ms)
• stream.read_exactly!(bytes, timeout_ms)
• stream.read_until!(delimiter, max_bytes, timeout_ms)
• stream.read_line!(max_bytes, timeout_ms)
• stream.write!(bytes, timeout_ms)
• stream.write_utf8!(text, timeout_ms)

There are no unbounded or separately named timeout methods to remove later.

Testing

• cargo test --locked --lib
• ./scripts/test.py --operation validate
• ./scripts/test.py --operation build --no-build
• ./scripts/test.py --operation run --target x64musl
• generated Rust glue check

Closes #437