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>

cmd/tailscale/cli/cli_test.go

@@ -1533,13 +1533,13 @@ func TestParseNLArgs(t *testing.T) {
 			parseDisablements: true,
 		},
 		{
-			name:      "key no votes",
+			name:      "key-no-votes",
 			input:     []string{"nlpub:" + strings.Repeat("00", 32)},
 			parseKeys: true,
 			wantKeys:  []tka.Key{{Kind: tka.Key25519, Votes: 1, Public: bytes.Repeat([]byte{0}, 32)}},
 		},
 		{
-			name:      "key with votes",
+			name:      "key-with-votes",
 			input:     []string{"nlpub:" + strings.Repeat("01", 32) + "?5"},
 			parseKeys: true,
 			wantKeys:  []tka.Key{{Kind: tka.Key25519, Votes: 5, Public: bytes.Repeat([]byte{1}, 32)}},
@@ -1551,13 +1551,13 @@ func TestParseNLArgs(t *testing.T) {
 			wantDisablements:  [][]byte{bytes.Repeat([]byte{2}, 32), bytes.Repeat([]byte{3}, 32)},
 		},
 		{
-			name:      "disablements not allowed",
+			name:      "disablements-not-allowed",
 			input:     []string{"disablement:" + strings.Repeat("02", 32)},
 			parseKeys: true,
 			wantErr:   fmt.Errorf("parsing key 1: key hex string doesn't have expected type prefix tlpub:"),
 		},
 		{
-			name:              "keys not allowed",
+			name:              "keys-not-allowed",
 			input:             []string{"nlpub:" + strings.Repeat("02", 32)},
 			parseDisablements: true,
 			wantErr:           fmt.Errorf("parsing argument 1: expected value with \"disablement:\" or \"disablement-secret:\" prefix, got %q", "nlpub:0202020202020202020202020202020202020202020202020202020202020202"),