uuid: introduce and use luaL_pushuuidstr()

The function safely pushes tt_uuid as a string on a Lua stack.
Safety means that it does not use tt_uuid_str() which stores the
result into the global static buffer and can not be used in Lua
context.

The static buffer is not safe to use in Lua and Lua C because
during a static string push onto a Lua stack the GC might be
started and it can spoil the buffer.

Part of #6259