3c5dc9d581
Commit 79685cbe (AF_INET6 socket support) introduced
String::with_capacity() at socket.rs:80 but only imported
ToString from alloc::string, not String itself. This caused
E0433 'cannot find type String in this scope' during canonical
build (edition 2024 with -Z build-std).
Fix: add String to the existing alloc::string import.