fix: Convert vendor/pezkuwi-subxt from submodule to regular directory

vendor/pezkuwi-subxt/LICENSE

@@ -0,0 +1,17 @@
+Copyright 2019-2025 Parity Technologies (UK) Ltd.
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of (at your option) either the Apache License,
+Version 2.0, or the GNU General Public License as published by the
+Free Software Foundation, either version 3 of the License, or (at your
+option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+
+For details and specific language governing permissions and
+limitations, see either
+
+ - http://www.gnu.org/licenses/ for the GNU GPL
+ - http://www.apache.org/licenses/LICENSE-2.0 for the Apache license