server/grpc: add configurable graceful shutdown timeout (v4 & v5)

[Grantmartin2002]

Summary

• Add GracefulStopTimeout server option to configure how long the gRPC server waits for in-flight requests to complete during graceful shutdown
• Applied to both v4 and v5 plugins
• Defaults to time.Second for backwards compatibility

Problem

The gRPC server has a hardcoded 1-second timeout after calling GracefulStop() before forcefully calling Stop(). For applications with long-lived gRPC streams (e.g., server-side streaming in Kubernetes), this causes active streams to be terminated with ECONNRESET during rolling updates, even when terminationGracePeriodSeconds allows for graceful draining.

Usage

import (
    grpcsrv "github.com/go-micro/plugins/v4/server/grpc"
)

srv := micro.NewService(
    micro.Server(grpcsrv.NewServer(
        grpcsrv.GracefulStopTimeout(3 * time.Minute),
    )),
)

Changes

• v4/server/grpc/options.go — add GracefulStopTimeout option and context key
• v4/server/grpc/grpc.go — read option, fall back to time.Second
• v5/server/grpc/options.go — same
• v5/server/grpc/grpc.go — same

Fixes #162