feat(lexer, preprocessor): replace cstring conversion with copy and refactor macro expansion

- Replace `scc_cstring_from_cstr(scc_cstring_as_cstr(...))` with `scc_cstring_copy()` in lexer to fix memory leaks
- Extract macro expansion logic into separate `expand_macro.c` file
- Remove `expand_stack` parameter from `scc_pp_expand_macro()` function
- Add new parsing functions for macro replacement lists and arguments
- Add string utility functions for whitespace trimming and string joining
- Update memory stream documentation for clarity

libs/pprocessor/include/pp_parse.h

@@ -5,9 +5,14 @@
 #include <pp_macro.h>
 void scc_pp_parse_directive(scc_probe_stream_t *stream, scc_pos_t *pos,
                             scc_pp_macro_table_t *macros);
+cbool scc_pp_parse_macro_replace_list(scc_probe_stream_t *stream,
+                                      scc_pp_macro_list_t *list);
+cbool scc_pp_parse_macro_arguments(scc_probe_stream_t *stream,
+                                   scc_pp_macro_list_t *args);
+
+// expand
 cbool scc_pp_expand_macro(scc_probe_stream_t *stream,
                           scc_pp_macro_table_t *macros,
-                          scc_pp_macro_table_t *expand_stack,
                           scc_probe_stream_t **out_stream, int depth);
 
 #endif /* __SCC_PP_PARSE_H__ */