cmd/vet: add subtestnames analyzer; fix all existing violations

Add a new vet analyzer that checks t.Run subtest names don't contain
characters requiring quoting when re-running via "go test -run". This
enforces the style guide rule: don't use spaces or punctuation in
subtest names.

The analyzer flags:
- Direct t.Run calls with string literal names containing spaces,
  regex metacharacters, quotes, or other problematic characters
- Table-driven t.Run(tt.name, ...) calls where tt ranges over a
  slice/map literal with bad name field values

Also fix all 978 existing violations across 81 test files, replacing
spaces with hyphens and shortening long sentence-like names to concise
hyphenated forms.

Updates #19242

Change-Id: Ib0ad96a111bd8e764582d1d4902fe2599454ab65
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

k8s-operator/reconciler/proxygrouppolicy/proxygrouppolicy_test.go

@@ -30,7 +30,7 @@ func TestReconciler_Reconcile(t *testing.T) {
 		ExpectsError        bool
 	}{
 		{
-			Name:                "single policy, denies all",
+			Name:                "single-policy-denies-all",
 			ExpectedPolicyCount: 2,
 			Request: reconcile.Request{
 				NamespacedName: types.NamespacedName{
@@ -53,7 +53,7 @@ func TestReconciler_Reconcile(t *testing.T) {
 			},
 		},
 		{
-			Name:                "multiple policies merged",
+			Name:                "multiple-policies-merged",
 			ExpectedPolicyCount: 2,
 			Request: reconcile.Request{
 				NamespacedName: types.NamespacedName{
@@ -89,7 +89,7 @@ func TestReconciler_Reconcile(t *testing.T) {
 			},
 		},
 		{
-			Name:                "no policies, no child resources",
+			Name:                "no-policies-no-child-resources",
 			ExpectedPolicyCount: 0,
 			Request: reconcile.Request{
 				NamespacedName: types.NamespacedName{