fix(run): migrate grpc server and remove deprecated calls

[amcolin]

Description

This PR modernizes our gRPC client implementation and proto-timestamp handling. It removes several heavily deprecated APIs (such as grpc.Dial, grpc.WithInsecure(), and the legacy ptypes package) and aligns our codebase with the standards required by gRPC v1.80.0 and flagged as vulnerability alerts:

• chore(deps): bump google.golang.org/grpc from 1.72.1 to 1.79.3 in /run/service-health #5482
• https://github.com/GoogleCloudPlatform/golang-samples/security/dependabot/2407 2407
• https://github.com/GoogleCloudPlatform/golang-samples/security/dependabot/2345 2345
• https://github.com/GoogleCloudPlatform/golang-samples/security/dependabot/2343 2343

Additionally, it resolves a potential memory leak in our streaming endpoint by switching from loop-bound time.After channels to a reusable time.Ticker.

Fixes Internal: b/513615351

Checklist

• I have followed Contributing Guidelines from CONTRIBUTING.MD
• Tests pass: go test -v ./.. (see Testing)
• Code formatted: gofmt (see Formatting)
• Vetting pass: go vet (see Formatting)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[gemini-code-assist]

Code Review

This pull request performs a comprehensive update of Go dependencies across several modules, including custom-metrics, grpc-ping, grpc-server-streaming, and service-health. Key changes include migrating from the deprecated ptypes package to google.golang.org/protobuf, updating gRPC connection methods from grpc.Dial to grpc.NewClient, and refactoring the streaming server to use time.Ticker for better resource management. Review feedback identifies high-severity issues where insufficient error handling after connection attempts could lead to nil pointer panics during deferred cleanup. Additionally, it is recommended to use generated protobuf getters to safely access nested fields and avoid potential panics.