golang, libgolang: Add byte / rune types

Those types are the base when working with byte- and unicode strings.
It will be clearer to use them explicitly instead of uint8_t and int32_t
when processing string.

golang/_golang.pxd

 # cython: language_level=2
-# Copyright (C) 2019-2022  Nexedi SA and Contributors.
+# Copyright (C) 2019-2023  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -65,6 +65,9 @@ cdef extern from *:
 # on the edge of Python/nogil world.
 from libcpp.string cimport string  # golang::string = std::string
 cdef extern from "golang/libgolang.h" namespace "golang" nogil:
+    ctypedef unsigned char  byte
+    ctypedef signed int     rune  # = int32
+
     void panic(const char *)
     const char *recover()
 

golang/libgolang.h

@@ -438,6 +438,10 @@ constexpr Nil nil = nullptr;
 // string is alias for std::string.
 using string = std::string;
 
+// byte/rune types related to string.
+using byte = uint8_t;
+using rune = int32_t;
+
 // func is alias for std::function.
 template<typename F>
 using func = std::function<F>;