chore: 完成项目汉化与测试覆盖增强

- 将项目文档、注释全量翻译为简体中文
- 新增 coverage 配置并要求 100% 分支覆盖率
- 补充所有模块的单元测试用例，覆盖全分支场景
- 重构执行器代码，提取公共重试与失败逻辑

pyproject.toml

@@ -70,3 +70,13 @@ url     = "https://mirrors.aliyun.com/pypi/simple/"
 
 [dependency-groups]
 dev = ["pyflowx[dev]"]
+
+[tool.coverage.run]
+branch      = true
+concurrency = ["greenlet", "thread"]
+source      = ["pyflowx"]
+
+[tool.coverage.report]
+exclude_lines = ["if TYPE_CHECKING:", "if __name__ == .__main__.:", "pragma: no cover", "raise NotImplementedError"]
+fail_under    = 100
+show_missing  = true