fix(test): make extensions analytics test tolerant of nil snapshot slice

Three CI fixes:

1. extensions_cache_invalidation_test.go: TestExtensionsCacheInvalidation
   Analytics/records_no_MutationEvent_when_extension_delete_is_skipped
   asserted assert.Equal([]MutationEvent{}, stats.MutationEvents). The
   snapshot's slices.Clone returns nil when the underlying slice is
   never appended to, so DeepEqual mismatched the empty-slice expected
   value against the nil actual. Switch to len() == 0, which is exact
   and tolerates the nil/empty implementation detail.

2. cache_key_parity_test.go: gci import grouping fix per .golangci.yml
   sections (standard / default / wundergraph / wundergraph/graphql-go-tools).

3. planner_test.go: gofmt -s fix for redundant []int{0} slice literals
   in the reused-planner regression test.

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

Author: jensneuse

v2/pkg/engine/plan/planner_test.go

@@ -971,8 +971,8 @@ func TestPlanner_Plan(t *testing.T) {
 			},
 		}, costHashes(plan2))
 		assert.Equal(t, map[int][]int{
-			0: []int{0},
-			1: []int{0},
+			0: {0},
+			1: {0},
 		}, sharedPlanner.planningVisitor.fieldPlanners)
 	})
 

v2/pkg/engine/resolve/cache_key_parity_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/golang/mock/gomock"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
 	"github.com/wundergraph/astjson"
 	"github.com/wundergraph/go-arena"
 

v2/pkg/engine/resolve/extensions_cache_invalidation_test.go

@@ -240,7 +240,10 @@ func TestExtensionsCacheInvalidationAnalytics(t *testing.T) {
 		env.run()
 		stats := env.ctx.GetCacheStats()
 
-		assert.Equal(t, []MutationEvent{}, stats.MutationEvents)
+		// Snapshot's slices.Clone returns nil when the underlying slice is nil
+		// (no events appended). Assert the count rather than DeepEqual against
+		// []MutationEvent{}, which would mismatch a nil slice.
+		assert.Equal(t, 0, len(stats.MutationEvents))
 	})
 }