Fix flaky gRPC client tests in sidecar

Add grpc.WaitForReady(true) option to test client connections to handle
race conditions where the gRPC server starts slower than client calls.
This eliminates timing-based test failures in sidecar/internal/reconciler
tests.

The WaitForReady option ensures the client waits for the server to be
ready before sending RPCs, rather than failing immediately if the
connection is not yet established.

Author: irek02

sidecar/internal/test/rpc.go

@@ -89,5 +89,9 @@ func ClientConn(tmpSockUri string) (*grpc.ClientConn, error) {
 	return grpc.NewClient(tmpSockUri,
 		// nothing fancy for unit tests
 		grpc.WithTransportCredentials(insecure.NewCredentials()),
+		grpc.WithDefaultCallOptions(
+			// Handle server starting slower than client calls in tests
+			grpc.WaitForReady(true),
+		),
 	)
 }