Prepare for FFI migration: use cdata for struct tuple.

src/box/CMakeLists.txt

src/box/lua/call.cc

src/box/lua/tuple.cc

src/box/lua/tuple.lua

src/lua/utils.c

src/lua/utils.h

test/box/net.box.result

test/box/tuple.result

third_party/lua-yaml/lyaml.c