fix: flake8 F811 unused reimport + F541 f-string without placeholders

tests/render_compare/audio_diff.py

@@ -255,7 +255,6 @@ def _probe_audio_info(file_path: str) -> dict[str, int]:
             text=True,
             timeout=10,
         )
-        import json
 
         info = json.loads(result.stdout)
         stream = info.get("streams", [{}])[0]

tests/render_compare/runner.py

@@ -245,7 +245,7 @@ class CompareRunner:
 
             if not (result.legacy_success and result.unified_success):
                 result.error = f"Legacy success={result.legacy_success}, Unified success={result.unified_success}"
-                print(f"  ⚠️  任务未全部成功，跳过对比")
+                print("  ⚠️  任务未全部成功，跳过对比")
                 return result
 
             # 3. 下载视频
@@ -348,7 +348,7 @@ class CompareRunner:
                         percentage=orig.get("percentage", 0),
                         whitelist=orig.get("whitelist"),
                     )
-                    print(f"\n[flag_mode] ✅ 已恢复原始 Feature Flag 配置")
+                    print("\n[flag_mode] ✅ 已恢复原始 Feature Flag 配置")
                 except Exception as e:
                     print(f"\n[flag_mode] ❌ 恢复 Feature Flag 失败: {e}")
                     print("  请手动检查并恢复 render_engine flag 配置！")