Bundle LZMA SDK for .edz extraction; drop 7z CLI dependency (M3)

Replaces the QProcess->7z shim with the public-domain LZMA SDK (23.01) 7-Zip
reader, vendored under sources/import/edz/lzma/ (decode-only subset). New
edzsevenzip.cpp wraps SzArEx_Open/SzArEx_Extract and writes entries via Qt, so
EdzArchive no longer needs an external 7-Zip at runtime. Enables the C language
in CMake for the vendored sources.

Verified: the bundled decoder extracts all three ifm sample .edz and the
generated elements still match the Python oracle exactly (byte-correct decode),
with no 7z on the path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sources/import/edz/edzsevenzip.h

@@ -0,0 +1,31 @@
+/*
+	Copyright 2006 The QElectroTech Team
+	This file is part of QElectroTech.
+
+	QElectroTech is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 2 of the License, or
+	(at your option) any later version.
+
+	QElectroTech 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. See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with QElectroTech. If not, see <http://www.gnu.org/licenses/>.
+*/
+#ifndef EDZSEVENZIP_H
+#define EDZSEVENZIP_H
+
+#include <QString>
+
+/**
+	Extract every entry of the 7-Zip archive at @a archivePath into @a destDir,
+	using the bundled (public-domain) LZMA SDK — no external 7-Zip needed.
+	@return true on success; on failure @a error explains why.
+*/
+bool sevenZipExtract(const QString &archivePath, const QString &destDir,
+		     QString &error);
+
+#endif // EDZSEVENZIP_H