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

runtime/libutils/include/strpool.h

@@ -8,7 +8,7 @@
 #ifndef __SCC_STRPOOL_H__
 #define __SCC_STRPOOL_H__
 
-#include "hashmap.h"
+#include "hashtable.h"
 #include <libcore.h>
 
 /**