Resolve Client.Go-004..010 code-review findings

Client.Go-004: ran gofmt on alarms_test.go and galaxy_test.go; the tree is
now gofmt-clean.

Client.Go-005/009/010: migrated Dial/DialGalaxy off the deprecated
grpc.DialContext/WithBlock to grpc.NewClient via a shared dial helper, with
a DialTimeout-bounded readiness probe to keep fail-fast semantics; shared
callContext deadline arithmetic; updated the stale Dial doc comment. Test
harnesses use passthrough:///bufnet for the NewClient default-scheme change.

Client.Go-006: added GatewayError.Code() and an IsTransient(err) helper so
callers can classify transient gRPC failures.

Client.Go-007: newCorrelationID no longer returns an empty id when
crypto/rand fails — it falls back to a non-empty time+counter id.

Client.Go-008: added coverage_test.go for transport-credential resolution,
callContext deadline arithmetic, and native value/array edge kinds.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/go/mxgateway/galaxy_test.go

@@ -55,8 +55,8 @@ func TestGalaxyGetLastDeployTimeReturnsTimestampWhenPresent(t *testing.T) {
 	want := time.Date(2026, 4, 28, 12, 34, 56, 0, time.UTC)
 	fake := &fakeGalaxyServer{
 		deployReply: &pb.GetLastDeployTimeReply{
-			Present:           true,
-			TimeOfLastDeploy:  timestamppb.New(want),
+			Present:          true,
+			TimeOfLastDeploy: timestamppb.New(want),
 		},
 	}
 	client, cleanup := newGalaxyBufconnClient(t, fake)
@@ -348,8 +348,10 @@ func newGalaxyBufconnClient(t *testing.T, fake *fakeGalaxyServer) (*GalaxyClient
 	dialer := func(ctx context.Context, _ string) (net.Conn, error) {
 		return listener.DialContext(ctx)
 	}
+	// grpc.NewClient defaults to the dns scheme; use passthrough so the
+	// bufconn fake target reaches the context dialer unresolved.
 	client, err := DialGalaxy(context.Background(), Options{
-		Endpoint:  "bufnet",
+		Endpoint:  "passthrough:///bufnet",
 		APIKey:    "test-api-key",
 		Plaintext: true,
 		DialOptions: []grpc.DialOption{