fix: audit fix — reduce password copies in memory (v0.8.4)

- attempt_login takes Zeroizing<String> by value, eliminating the redundant
  Zeroizing::new(password.to_string()) that doubled the Rust-owned copy.
- Clear password_entry's internal buffer immediately after extracting the
  password, shortening the window during which the GTK GString persists in
  non-zeroizable libc memory.

src/greeter.rs

@@ -493,6 +493,10 @@ pub fn create_greeter_window(
             let Some(user) = user else { return };
 
             let password = Zeroizing::new(entry.text().to_string());
+            // Clear the GTK entry's internal buffer as early as possible. GTK allocates
+            // the backing `GString` via libc malloc, which `zeroize` cannot reach — the
+            // best we can do is shorten the window during which it resides in memory.
+            entry.set_text("");
 
             let session = get_selected_session(&session_dropdown, &sessions_rc);
             let Some(session) = session else {
@@ -502,7 +506,7 @@ pub fn create_greeter_window(
 
             attempt_login(
                 &user,
-                &password,
+                password,
                 &session,
                 strings,
                 &state,
@@ -953,7 +957,7 @@ fn set_login_sensitive(
 #[allow(clippy::too_many_arguments)]
 fn attempt_login(
     user: &User,
-    password: &str,
+    password: Zeroizing<String>,
     session: &Session,
     strings: &'static Strings,
     state: &Rc<RefCell<GreeterState>>,
@@ -992,7 +996,6 @@ fn attempt_login(
     set_login_sensitive(password_entry, session_dropdown, false);
 
     let username = user.username.clone();
-    let password = Zeroizing::new(password.to_string());
     let exec_cmd = session.exec_cmd.clone();
     let session_name = session.name.clone();
     let greetd_sock = state.borrow().greetd_sock.clone();