feat: add several metrics related to CDN request counts

[DDDFiish]

添加了三个指标 cdnStatusCount cdnBackSourceStatusCount cdnHitTotal
分别表示 cdn状态码数量、cdn回源状态码数量、cdn缓存命中次数

revert #14 里面的更改，exporter暴露的命中率采用官方的计算方式

[Copilot]

Pull request overview

This pull request adds three new CDN metrics to the upyun-exporter: cdnStatusCount, cdnBackSourceStatusCount, and cdnHitTotal. The changes include upgrading dependencies (Go version from 1.18 to 1.23.0, Prometheus client from v1.13.0 to v1.23.2), adding new metric descriptors and collection logic, improving terminology in metric descriptions, and modifying the CDN hit rate calculation logic.

Changes:

• Added three new Prometheus metrics for CDN status code counts and cache hit totals
• Updated Go version and Prometheus client library dependencies
• Modified CDN hit rate calculation to exclude 403 status codes
• Improved metric description terminology from "概率" (probability) to "比例" (proportion)

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 6 comments.

File	Description
main.go	Reorganized imports to separate standard library from third-party packages
go.mod	Updated Go version to 1.23.0 and upgraded Prometheus client_golang to v1.23.2, includes incorrect module path for yaml/v2
go.sum	Updated dependency checksums for new versions, includes incorrect module path for yaml/v2
exporter/exporter.go	Added three new metric descriptors, implemented collection logic for status counts and hit totals, modified hit rate calculation, improved metric descriptions

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[DDDFiish]

@LeoQuote 有空帮忙看一下

[LeoQuote]

@DDDFiish lint 要再修一下, golang 的版本看看有没有遗漏的地方