fix: P1审查修复 — error.c arena化 + Self类型解析 + trait查找加固 + 缓冲区安全

P1-①: error_init/add 从 malloc/realloc/strdup 改为 arena_alloc/arena_strdup
P1-②: impl 方法中 Self 类型在 sema 解析为实际结构体名
P1-③: trait 方法 fallback 增加前缀校验(strncmp)，method_name 统一更新
P1-④: codegen args[16] 增加溢出检查，移除 parser 未使用的 mods/uses 数组
新增: 36_self_type.l 集成测试（Self 类型 + trait 方法）

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/driver/error.c

@@ -1,22 +1,25 @@
 #include "error.h"
+#include "arena.h"
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdarg.h>
 #include <string.h>
 
-void error_init(ErrorList* list) {
-    list->capacity = 8;
-    list->errors = malloc(list->capacity * sizeof(ErrorInfo));
+void error_init(ErrorList* list, Arena* a) {
+    list->capacity = 64;
+    list->errors = arena_alloc(a, list->capacity * sizeof(ErrorInfo));
     list->count = 0;
+    list->arena = a;
     if (!list->errors) list->capacity = 0;
 }
 
 void error_add(ErrorList* list, const char* filename, int line, int col, const char* fmt, ...) {
     if (!list->errors) return;
     if (list->count >= list->capacity) {
-        size_t new_cap = list->capacity * 2;
-        ErrorInfo* new_errs = realloc(list->errors, new_cap * sizeof(ErrorInfo));
+        size_t new_cap = list->capacity + 64;
+        ErrorInfo* new_errs = arena_alloc(list->arena, new_cap * sizeof(ErrorInfo));
         if (!new_errs) return;
+        memcpy(new_errs, list->errors, list->capacity * sizeof(ErrorInfo));
         list->errors = new_errs;
         list->capacity = new_cap;
     }
@@ -26,12 +29,9 @@ void error_add(ErrorList* list, const char* filename, int line, int col, const c
     int n = vsnprintf(buf, sizeof(buf), fmt, args);
     va_end(args);
     if (n < 0) return;
-    char* msg = strdup(buf);
-    char* fname = strdup(filename);
-    if (!msg || !fname) {
-        free(msg); free(fname);
-        return;
-    }
+    char* msg = arena_strdup(list->arena, buf);
+    char* fname = arena_strdup(list->arena, filename);
+    if (!msg || !fname) return;
     list->errors[list->count++] = (ErrorInfo){
         .message = msg,
         .filename = fname,