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/hashtable.h

@@ -1,12 +1,12 @@
 /**
- * @file hashmap.h
+ * @file hashtable.h
  * @brief 开放寻址法哈希表实现
  *
  * 提供基于向量容器的哈希表实现，支持动态扩容和墓碑机制
  */
 
-#ifndef __SCC_HASHMAP_H__
-#define __SCC_HASHMAP_H__
+#ifndef __SCC_HASHTABLE_H__
+#define __SCC_HASHTABLE_H__
 
 #include <libcore.h>
 
@@ -121,4 +121,4 @@ typedef int (*scc_hashtable_iter_fn)(const void *key, void *value,
 void scc_hashtable_foreach(scc_hashtable_t *ht, scc_hashtable_iter_fn iter_func,
                            void *context);
 
-#endif /* __SCC_HASHMAP_H__ */
+#endif /* __SCC_HASHTABLE_H__ */

runtime/libutils/include/libutils.h

@@ -1,9 +1,9 @@
 #ifndef __SMCC_UTILS_H__
 #define __SMCC_UTILS_H__
 
-#include "hashmap.h"
+#include "hashtable.h"
 #include "kllist.h"
 #include "strpool.h"
 #include <libcore.h>
 
-#endif // __SMCC_UTILS_H__
+#endif /* __SMCC_UTILS_H__ */

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>
 
 /**