Deprecate github.com/dubbogo/grpc-go usage

[Alanxtl]

Background

dubbo-go currently depends on github.com/dubbogo/grpc-go, while the upstream and actively maintained module is google.golang.org/grpc / github.com/grpc/grpc-go.

We should deprecate and remove the usage of github.com/dubbogo/grpc-go to avoid staying on a forked dependency and to align with the upstream gRPC Go ecosystem.

Current usage

A quick scan shows the dependency is still present in multiple places:

• go.mod depends on github.com/dubbogo/grpc-go v1.42.10
• Triple/Dubbo3 protocol code imports github.com/dubbogo/grpc-go, including metadata, codes, and status
• generated compatibility files still reference github.com/dubbogo/grpc-go
• tools/protoc-gen-go-triple and tools/dubbogo-cli templates/generators still emit github.com/dubbogo/grpc-go

Expected work

• Replace runtime imports from github.com/dubbogo/grpc-go with the upstream gRPC Go module where compatible.
• Update code generation templates so newly generated Triple code no longer imports github.com/dubbogo/grpc-go.
• Regenerate or update checked-in generated files that currently reference the fork.
• Remove github.com/dubbogo/grpc-go from go.mod / go.sum once no longer used.
• Add or update tests that cover Triple/Dubbo3 compatibility after the migration.

Acceptance criteria

• rg "github.com/dubbogo/grpc-go" returns no runtime or generated-code references, except possibly historical docs/changelog entries if intentionally kept.
• go mod tidy no longer keeps github.com/dubbogo/grpc-go in the module graph.
• Existing Triple/Dubbo3 protocol tests and generator tests continue to pass.