CVE-2026-68930 Russh: Channel-scoped server callbacks can be reached without an open channel

Russh is a Rust SSH client & server library. Prior to 0.62.5, russh dispatches channel-scoped Handler callbacks for recipient channel IDs that were never opened or confirmed in russh/src/server/encrypted.rs, serverreadauthenticated, and the execrequest callback. Version 0.62.5 fixes the issue...