Function push_fstring 

pub fn push_fstring<'a>(
    state: &mut LuaState,
    fmt: &[u8],
    args: &[FmtArg<'a>],
) -> Result<GcRef<LuaString>, LuaError>

Variadic entry point; delegates to push_vfstring.

Callers building an error message should prefer collapsing the call into LuaError::runtime(format_args!(...)) instead.