fix: a panic on one thread no longer takes the whole app down

Every shared lock was std::sync::Mutex with lock().unwrap() (~150 sites),
so a panic in any session's reader or callback poisoned the lock and the
next UI frame panicked too, dropping every open session. Locks are now
parking_lot::Mutex (no poisoning; already in the dependency tree), and a
panic hook reports worker panics as an error toast instead of the session
silently stopping (F3, F4).

rust/core/Cargo.toml

@@ -22,6 +22,7 @@ sha2 = "0.11.0"
 hmac = "0.13.0"
 sha1 = "0.11.0"
 zeroize = "1"
+parking_lot = "0.12"
 portable-pty = "0.9.0"
 serialport = { version = "4", default-features = false }
 des = "0.9"