feat(probe): add Kubernetes probe support with liveness, readiness, and startup checks

[Alanxtl]

This is the implemention of #2039
which is the rewritten of #3047
usage are demonstrated in apache/dubbo-go-samples#1033
docs are written in apache/dubbo-website#3193

Kubernetes 探针（Probe）功能说明

本模块提供独立的 HTTP 探针服务，面向 Kubernetes 的 liveness、readiness、startup 三类探针。
它支持用户自定义健康检查逻辑，并可选择性地与 Dubbo Server 生命周期进行内部状态对齐。

设计目标

1. 可扩展：通过回调注册自定义检查逻辑。
2. 可控风险：liveness 默认不带内部逻辑，避免不当重启。
3. 生命周期对齐：readiness/startup 可选用内部状态。

默认 HTTP 路径

当启用 probe 后，默认在22222端口下暴露以下路径：

• GET /live：liveness 探针
• GET /ready：readiness 探针
• GET /startup：startup 探针

响应规则：

• 所有检查通过：HTTP 200
• 任一检查失败：HTTP 503

new api 配置方式

通过 metrics.NewOptions(...) 传入以下 Option 配置：

ins, err := dubbo.NewInstance(
  dubbo.WithMetrics(
    metrics.WithProbeEnabled(),
    metrics.WithProbePort(22222),
    metrics.WithProbeLivenessPath("/live"),
    metrics.WithProbeReadinessPath("/ready"),
    metrics.WithProbeStartupPath("/startup"),
    metrics.WithProbeUseInternalState(true),
  ),
)

old api 配置方式

在 metrics 配置下新增 probe 子配置：

metrics:
  probe:
    enabled: true
    port: "22222"
    liveness-path: "/live"
    readiness-path: "/ready"
    startup-path: "/startup"
    use-internal-state: true

配置项说明：

• enabled：是否开启 probe 服务
• port：probe HTTP 端口
• liveness-path：liveness 路径
• readiness-path：readiness 路径
• startup-path：startup 路径
• use-internal-state：是否启用内部生命周期状态检查，默认启用

内部状态（UseInternalState）

当 use-internal-state: true 时，探针会附加内部状态检查：

• readiness 依赖 probe.SetReady(true/false)
• startup 依赖 probe.SetStartupComplete(true/false)

默认行为：

• 应用启动完成后（Server.Serve() 成功执行）会设置 ready=true、startup=true
• 应用优雅关闭时会将 ready=false

如果设置为 false，则完全由用户注册的回调决定探针结果。

自定义健康检查（推荐）

通过注册回调即可扩展探针逻辑：

import "dubbo.apache.org/dubbo-go/v3/metrics/probe"

// liveness 例子
probe.RegisterLiveness("db", func(ctx context.Context) error {
    // 检查数据库连接
    return nil
})

// readiness 例子
probe.RegisterReadiness("cache", func(ctx context.Context) error {
    // 检查缓存或依赖中间件
    return nil
})

// startup 例子
probe.RegisterStartup("warmup", func(ctx context.Context) error {
    // 检查预热逻辑是否完成
    return nil
})

注意事项

• liveness 风险：liveness 失败会触发 Pod 重启，请谨慎设置，推荐仅用作进程/核心依赖检测。
• readiness 适配：可以关联注册中心、数据库、缓存、下游依赖等健康状态。
• startup 适配：建议用于冷启动、预热或依赖初始化场景。

Kubernetes 示例

livenessProbe:
  httpGet:
    path: /live
    port: 22222
  initialDelaySeconds: 5
  periodSeconds: 5
readinessProbe:
  httpGet:
    path: /ready
    port: 22222
  initialDelaySeconds: 5
  periodSeconds: 5
startupProbe:
  httpGet:
    path: /startup
    port: 22222
  failureThreshold: 30
  periodSeconds: 10

Description

Fixes # (issue)

Checklist

• I confirm the target branch is develop
• Code has passed local testing
• I have added tests that prove my fix is effective or that my feature works

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

Codecov Report

❌ Patch coverage is 46.42857% with 105 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.93%. Comparing base (60d1c2a) to head (53a5f19).
⚠️ Report is 735 commits behind head on develop.

Files with missing lines	Patch %	Lines
metrics/probe/server.go	0.00%	57 Missing ⚠️
metrics/options.go	0.00%	19 Missing ⚠️
config/metric_config.go	0.00%	8 Missing and 1 partial ⚠️
global/metric_config.go	63.63%	5 Missing and 3 partials ⚠️
compat.go	81.81%	2 Missing and 2 partials ⚠️
metrics/probe/probe.go	87.09%	2 Missing and 2 partials ⚠️
server/options.go	0.00%	1 Missing and 1 partial ⚠️
server/server.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3213      +/-   ##
===========================================
+ Coverage    46.76%   47.93%   +1.17%     
===========================================
  Files          295      467     +172     
  Lines        17172    33943   +16771     
===========================================
+ Hits          8031    16272    +8241     
- Misses        8287    16355    +8068     
- Partials       854     1316     +462     

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