feat: implement stale client removal after timeout

- add goroutine to remove stale clients from the connection pool
- update client struct to track `LastPong` time
- set write deadline for websocket connections
- move package variables and const to `vars.go`
- log additional information when broadcasting errors

🤖

internal/websocket/vars.go

@@ -0,0 +1,18 @@
+package websocket
+
+import (
+	"net"
+	"sync"
+
+	"git.smsvc.net/pomodoro/GoTomato/pkg/models"
+)
+
+const SEND_TIMEOUT = 10
+const STALE_CLIENT_TIMEOUT = 90
+const STALE_CHECK_INTERVALL = 30
+
+// Clients is a map of connected WebSocket clients, where each client is represented by the WebsocketClient struct
+var Clients = make(map[net.Addr]*models.WebsocketClient)
+
+// Mutex to protect access to the Clients map
+var mu sync.Mutex