Deprecate github.com/dubbogo/grpc-go usage

## 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.