增强配置解析诊断信息

[ghangz]

这个改动增强了配置解析阶段的容错和定位能力，既能更稳妥地解析指标类型，也能正确处理带缩进的注释行和 UTF-8 配置文件，减少配置问题被误判成运行时异常的情况。

相关单元测试已经补充并通过，覆盖了不支持的指标类型、带缩进注释和 UTF-8 配置读取场景。

[gemini-code-assist]

Code Review

This pull request introduces configuration diagnostics to the exporter by extracting CSV validation and loading logic into a new config_loader module, accompanied by unit tests. It ensures that startup fails immediately if no valid metrics are loaded. The review feedback highlights several robust improvements: handling potential KeyError exceptions when dynamically resolving metric functions from globals(), explicitly specifying utf-8 encoding when opening the configuration file to prevent cross-platform decoding issues, and stripping leading whitespace before checking for comment lines.

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[gemini-code-assist]

在 init_required_metrics 中，metric_func = globals()[row[1]] 这一行位于 try-except 块之外。如果配置文件中包含未导入的指标类型（例如 Summary、Histogram 或 Info，虽然它们在 self.metric_types 中被声明为支持，但实际上并未在文件顶部导入），此处会抛出 KeyError 并导致 exporter 启动崩溃。

此外，为了完整支持 Summary、Histogram 和 Info 等指标类型，建议在获取指标函数时，如果 globals() 中不存在，则尝试从 prometheus_client 动态获取，并将该查找过程放入 try-except 块中，以确保即使遇到不支持的类型也能够优雅地记录错误并跳过，而不是直接崩溃。

Suggested change

	metric_func = globals()[row[1]]
	metric_name = row[2]
	metric_description = row[3]
	metric_labels = row[4:]
	try:
	self.metrics_required[metric_id] = metric_func(metric_name, metric_description, metric_labels)
	except Exception as e:
	print("Create metric exception: %s" % (e))
	metric_name = row[2]
	metric_description = row[3]
	metric_labels = row[4:]
	try:
	if row[1] not in globals():
	import prometheus_client
	metric_func = getattr(prometheus_client, row[1])
	else:
	metric_func = globals()[row[1]]
	self.metrics_required[metric_id] = metric_func(metric_name, metric_description, metric_labels)
	except (AttributeError, KeyError):
	print("Unsupported metric type: %s" % row[1])
	except Exception as e:
	print("Create metric exception: %s" % (e))

[gemini-code-assist]

在打开配置文件时，建议显式指定 encoding="utf-8"。在不同的操作系统或区域设置下，默认的系统编码可能不是 UTF-8（例如在某些 Windows 环境下默认是 GBK），这可能会导致读取包含中文注释或描述的 CSV 配置文件时发生 UnicodeDecodeError。显式指定编码可以提高代码的跨平台鲁棒性。

Suggested change

	with open(config_file, "r", newline="") as file_handle:
	with open(config_file, "r", newline="", encoding="utf-8") as file_handle:

[gemini-code-assist]

在判断是否为注释行时，使用 row[0].startswith("#")。如果用户在 CSV 文件的注释行前不小心留有空格（例如 # comment），该行将无法被正确识别为注释行，从而可能导致解析错误。建议在判断前使用 .lstrip() 去除首部空格。

Suggested change

	if row[0].startswith("#"):
	if row[0].lstrip().startswith("#"):