feat(parse): implement # and ## operator handling in macro expansion

- Add support for # (stringify) and ## (concatenation) operators in macro replacement lists
- Implement scc_pp_expand_string_unsafe() to process operator tokens during macro expansion
- Add helper macros to identify blank, stringify, and concatenation tokens in replacement lists
- Include missing headers (ctype.h, string.h) for character handling functions
- Update object macro expansion to use new string expansion function instead of simple concatenation
- Improve whitespace handling in macro replacement parsing to prevent interference with operator processing

libs/pprocessor/tests/test_unit.c

@@ -90,7 +90,7 @@ static void test_define_concat_operator(void) {
     TEST_CASE("concatenation operator (##)");
     CHECK_PP_OUTPUT_EXACT("#define CONCAT(a,b) a##b\nCONCAT(hello,world)\n",
                           "helloworld\n");
-    CHECK_PP_OUTPUT_EXACT("#define JOIN(pre,suf) pre##suf\nJOIN(var,123)\n",
+    CHECK_PP_OUTPUT_EXACT("#define JOIN(pre,suf) pre ## suf\nJOIN(var, 123)\n",
                           "var123\n");
 }