qrcodemodel: Rate limit the emission of reselect auth mode events

When hitting the Enter key for a while, bubbletea sends lots of events
and we may imply sending reselectAuthMode{} events faster than we can
actually handle the cancellation/reauthModeSelection in the whole stack.

This never happened (ever) when using the example broker, but it may
actually happen in a real world scenario where the broker may not cancel
the requests quickly enough.

Do this instead of avoiding the handling of the reselectAuthMode event
because it's better to prevent bubbletea to break our (fragile) system.

pam/integration-tests/testdata/tapes/cli/qr_code.tape

@@ -47,17 +47,17 @@ Show
 
 Hide
 Enter
-Sleep 300ms
+Sleep 800ms
 Show
 
 Hide
 Enter
-Sleep 300ms
+Sleep 800ms
 Show
 
 Hide
 Enter
-Sleep 300ms
+Sleep 800ms
 Show
 
 Hide

pam/integration-tests/testdata/tapes/cli/qr_code_quick_regenerate.tape

@@ -52,8 +52,8 @@ Sleep 300ms
 Show
 
 Hide
-Enter@1ms 50
-Sleep 10s
+Enter@1ms 800
+Sleep 3s
 Show
 
 Sleep 300ms

pam/internal/adapter/qrcodemodel.go

@@ -1,23 +1,30 @@
 package adapter
 
 import (
+	"context"
 	"fmt"
 	"os"
 	"strings"
+	"time"
 
 	tea "github.com/charmbracelet/bubbletea"
 	"github.com/charmbracelet/lipgloss"
 	"github.com/muesli/termenv"
 	"github.com/skip2/go-qrcode"
 	"github.com/ubuntu/authd"
+	"github.com/ubuntu/authd/internal/log"
 )
 
 var centeredStyle = lipgloss.NewStyle().Align(lipgloss.Center, lipgloss.Top)
 
+// reselectionRateLimit is the amount of time (in ms) that we wait before regenerating the qrcode.
+const reselectionRateLimit = int64(300)
+
 // qrcodeModel is the form layout type to allow authenticating and return a challenge.
 type qrcodeModel struct {
-	label       string
-	buttonModel *buttonModel
+	label              string
+	buttonModel        *buttonModel
+	selectionTimestamp int64
 
 	content string
 	code    string
@@ -39,12 +46,13 @@ func newQRCodeModel(content, code, label, buttonLabel string, wait bool) (qrcode
 	}
 
 	return qrcodeModel{
-		label:       label,
-		buttonModel: button,
-		content:     content,
-		code:        code,
-		qrCode:      qrCode,
-		wait:        wait,
+		label:              label,
+		buttonModel:        button,
+		selectionTimestamp: time.Now().UnixMilli(),
+		content:            content,
+		code:               code,
+		qrCode:             qrCode,
+		wait:               wait,
 	}, nil
 }
 
@@ -73,6 +81,12 @@ func (m qrcodeModel) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			if m.buttonModel == nil {
 				return m, nil
 			}
+			now := time.Now().UnixMilli()
+			if now-m.selectionTimestamp < reselectionRateLimit {
+				log.Debug(context.TODO(), "Button press ignored, too fast!")
+				return m, nil
+			}
+			m.selectionTimestamp = now
 			return m, sendEvent(reselectAuthMode{})
 		}
 	}