F-4971: zeroize stack ed448_key after Free in keygen_ed448 cleanup

wc_ed448_free does not zero the struct; add wc_ForceZero(&k, sizeof(k))
immediately after, matching the pattern used for ml_dsa (F-4972) and the
priv[] zeroing already present on the preceding line.

tools/keytools/keygen.c

@@ -859,6 +859,7 @@ cleanup:
     wc_ForceZero(priv, sizeof(priv));
     if (key_init == 0)
         wc_ed448_free(&k);
+    wc_ForceZero(&k, sizeof(k));
     if (exit_code != 0)
         exit(exit_code);
 }