fix(pr): report checks like gh, exit 8 while they are pending

tea pr checks printed relative links, "Error: pull request checks have
not all succeeded" with exit 1 for checks that were only pending, and
nothing at all without checks. It now heads the table with a colored
verdict and "0 failing, 1 successful, and 2 pending checks", prints a
status icon and absolute links, and exits 8 while checks are pending
and 1 when one failed, without an Error line (D21). clierr.Quiet
carries such an exit code past main without a message. Without checks
it says "no checks reported for pull request alice/x#8".

--watch redraws the summary in place on a terminal, and an expired
--timeout reads "timed out after 3s waiting for 2 pending checks". The
pull request argument is optional, and --web opens the pull request.

Signed-off-by: bircni <bircni@icloud.com>

internal/clierr/errors.go

@@ -14,9 +14,25 @@ const (
 	Usage          = 2
 	Canceled       = 3
 	Authentication = 4
-	Interrupted    = 130
+	// Pending reports checks that have not finished, like gh pr checks.
+	Pending     = 8
+	Interrupted = 130
 )
 
+// errReported is the message of Quiet errors.
+var errReported = errors.New("the command reported the outcome")
+
+// Quiet exits with code without an error message, for an outcome the command already reported,
+// such as failing checks.
+func Quiet(code int) error {
+	return &Error{Code: code, Err: errReported}
+}
+
+// IsQuiet reports whether err is a Quiet exit code.
+func IsQuiet(err error) bool {
+	return errors.Is(err, errReported)
+}
+
 // Error associates an operation error with a public CLI exit code.
 type Error struct {
 	Code int

internal/clierr/errors_test.go

@@ -27,6 +27,8 @@ func TestExitCodeDistinguishesCancellationAndInterruption(t *testing.T) {
 		{fmt.Errorf("draft preserved: %w", context.DeadlineExceeded), Canceled},
 		{Wrap(Interrupted, context.Canceled), Interrupted},
 		{errors.Join(errors.New("partial failure"), context.Canceled), Canceled},
+		{Quiet(Pending), Pending},
+		{fmt.Errorf("checks: %w", Quiet(Failure)), Failure},
 	} {
 		assert.Equal(t, test.code, ExitCode(test.err), "%v", test.err)
 	}