Include missing headers for compatibility with GCC 15

[pastalian]

cstdint needs to be included explicitly since GCC 15.
https://gcc.gnu.org/gcc-15/porting_to.html

/usr/bin/g++   -march=native -O3 -DNDEBUG -O3 -DNDEBUG -std=c++17 -MD -MT CMakeFiles/fsst.dir/libfsst.cpp.o -MF CMakeFiles/fsst.dir/libfsst.cpp.o.d -o CMakeFiles/fsst.dir/libfsst.cpp.o -c /fsst/libfsst.cpp
In file included from /fsst/libfsst.cpp:18:
/fsst/libfsst.hpp:39:9: error: ‘uint8_t’ does not name a type
   39 | typedef uint8_t u8;
      |         ^~~~~~~

/usr/bin/g++   -march=native -O3 -DNDEBUG -O3 -DNDEBUG -std=c++17 -MD -MT CMakeFiles/fsst12.dir/libfsst12.cpp.o -MF CMakeFiles/fsst12.dir/libfsst12.cpp.o.d -o CMakeFiles/fsst12.dir/libfsst12.cpp.o -c /fsst/libfsst12.cpp
In file included from /fsst/libfsst12.cpp:18:
/fsst/libfsst12.hpp:42:9: error: 'uint8_t' does not name a type
   42 | typedef uint8_t u8;
      |         ^~~~~~~