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>

sessionrecording/connect_test.go

@@ -35,7 +35,7 @@ func TestConnectToRecorder(t *testing.T) {
 		wantErr bool
 	}{
 		{
-			desc: "v1 recorder",
+			desc: "v1-recorder",
 			setup: func(t *testing.T) (*http.ServeMux, <-chan []byte) {
 				uploadHash := make(chan []byte, 1)
 				mux := http.NewServeMux()
@@ -50,7 +50,7 @@ func TestConnectToRecorder(t *testing.T) {
 			},
 		},
 		{
-			desc:  "v2 recorder",
+			desc:  "v2-recorder",
 			http2: true,
 			setup: func(t *testing.T) (*http.ServeMux, <-chan []byte) {
 				uploadHash := make(chan []byte, 1)
@@ -100,7 +100,7 @@ func TestConnectToRecorder(t *testing.T) {
 			},
 		},
 		{
-			desc:    "v2 recorder no acks",
+			desc:    "v2-recorder-no-acks",
 			http2:   true,
 			wantErr: true,
 			setup: func(t *testing.T) (*http.ServeMux, <-chan []byte) {