Fix build: tuple access syntax, namespace, LZ4 separate compilation

- miner.cpp: .get<N>() → std::get<N>() (boost::tuple member syntax
  doesn't exist on std::tuple)
- script.cpp: remove 'using namespace boost' (no boost headers left)
- smessage.cpp: include lz4/lz4.h instead of lz4/lz4.c (U64 typedef
  conflict with xxhash when LZ4 1.10.0 source included in same TU)
- makefile.unix: add obj/lz4.o as separate compilation unit
- triangles-qt.pro: add src/lz4/lz4.c to SOURCES

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

triangles-qt.pro

@@ -331,6 +331,7 @@ SOURCES += src/qt/triangles.cpp src/qt/trianglesgui.cpp \
     src/version.cpp \
     src/sync.cpp \
     src/smessage.cpp \
+    src/lz4/lz4.c \
     src/util.cpp \
     src/netbase.cpp \
     src/key.cpp \