chore: import upstream snapshot with attribution

examples/graceful-stop/README.md

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+# Graceful Stop Demo
+
+This example demonstrates the intended shutdown behavior after the gRPC graceful-stop patch.
+
+## Run
+
+```bash
+go run ./examples/graceful-stop
+```
+
+## Expected behavior
+
+- one long-running RPC starts
+- shutdown begins while that RPC is still running
+- new RPCs stop being accepted shortly after shutdown starts
+- the in-flight RPC is allowed to finish
+
+Typical output:
+
+```text
+long RPC is running; starting shutdown
+new RPC rejected after shutdown began: ...
+long RPC completed: slept for 1500ms
+done
+```
+
+There may be a small race window where the first post-stop RPC is still accepted once before subsequent new RPCs are rejected. The important part is that in-flight RPCs are drained while new RPCs are cut off.
+
+## Automated check
+
+```bash
+go test ./server/grpc -run TestGracefulStopRejectsNewRPCsButAllowsInFlightRPCs -v
+```
+
+## Environment
+
+- no special environment variables are required
+- the demo may print a TLS warning from `go-micro`; it is unrelated to this change