refactor: modernize Go version and go-kit internals

[crazyskinny]

Summary

• Upgrade the project Go version and align module/workspace configuration.
• Modernize Go idioms across packages and simplify implementation and test code.
• Refine Kratos adapters for auth, rate limiting, SSE, logging, and client IP handling.
• Update buf/code generation workflow, generated files, and examples.
• Use Redis UniversalClient in the rate limit store and cover construction through the public API.

Testing

• go test ./...
• go test ./kratos/...
• go test ./kratos/ratelimit/...
• git diff --check
• lint and formatting checks