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/lzma/7zBuf.h

@@ -0,0 +1,35 @@
+/* 7zBuf.h -- Byte Buffer
+2023-03-04 : Igor Pavlov : Public domain */
+
+#ifndef ZIP7_INC_7Z_BUF_H
+#define ZIP7_INC_7Z_BUF_H
+
+#include "7zTypes.h"
+
+EXTERN_C_BEGIN
+
+typedef struct
+{
+  Byte *data;
+  size_t size;
+} CBuf;
+
+void Buf_Init(CBuf *p);
+int Buf_Create(CBuf *p, size_t size, ISzAllocPtr alloc);
+void Buf_Free(CBuf *p, ISzAllocPtr alloc);
+
+typedef struct
+{
+  Byte *data;
+  size_t size;
+  size_t pos;
+} CDynBuf;
+
+void DynBuf_Construct(CDynBuf *p);
+void DynBuf_SeekToBeg(CDynBuf *p);
+int DynBuf_Write(CDynBuf *p, const Byte *buf, size_t size, ISzAllocPtr alloc);
+void DynBuf_Free(CDynBuf *p, ISzAllocPtr alloc);
+
+EXTERN_C_END
+
+#endif