fix: 5项立即修复 + 2项尽快修复

立即:
- lexer: token数组容量改为src_len+16 + idx越界防御
- symbol: 4个函数arena_alloc加NULL检查
- codegen: verify_err fallback用arena_strdup替代静态字符串
- codegen: cleanup_list从固定64改为arena动态扩容
- lexer: 标识符/字符串字面量65535字符上限

尽快:
- to_llvm_type: TYPE_STRUCT/TYPE_UNKNOWN/TYPE_ERROR显式case
- LLVMGetValueType2不存在(LLVM 22仍用旧名), 保留GlobalGetValueType

src/sema/symbol.c

@@ -4,6 +4,7 @@
 
 Scope* scope_new(void* alloc, Scope* parent) {
     Scope* s = (Scope*)arena_alloc_impl(alloc, sizeof(Scope));
+    if (!s) return NULL;
     s->head = NULL;
     s->parent = parent;
     return s;
@@ -26,6 +27,7 @@ Symbol* scope_insert(Scope* scope, void* alloc, const char* name,
         }
     }
     Symbol* sym = (Symbol*)arena_alloc_impl(alloc, sizeof(Symbol));
+    if (!sym) return NULL;
     sym->name = name; sym->kind = kind; sym->type = type;
     sym->is_mut = false; sym->return_type = TYPE_VOID;
     sym->param_types = NULL; sym->param_count = 0;
@@ -46,6 +48,7 @@ Symbol* scope_insert_function(Scope* scope, void* alloc, const char* name,
         }
     }
     Symbol* sym = (Symbol*)arena_alloc_impl(alloc, sizeof(Symbol));
+    if (!sym) return NULL;
     sym->name = name; sym->kind = SYM_FUNCTION; sym->type = TYPE_VOID;
     sym->return_type = ret; sym->param_types = pt; sym->param_count = pc;
     sym->struct_field_names = NULL;
@@ -66,6 +69,7 @@ Symbol* scope_insert_struct(Scope* scope, void* alloc, const char* name,
         }
     }
     Symbol* sym = (Symbol*)arena_alloc_impl(alloc, sizeof(Symbol));
+    if (!sym) return NULL;
     sym->name = name; sym->kind = SYM_STRUCT; sym->type = TYPE_STRUCT;
     sym->is_mut = false; sym->return_type = TYPE_VOID;
     sym->param_types = NULL; sym->param_count = 0;