GHSA-4xgv-j62q-h3rj: Panic during unmarshal of Hello Verify Request in github.com/pion/dtls/v2

The vulnerability stems from the Unmarshal method of MessageHelloVerifyRequest. The commit diff shows the fix explicitly modifies this function by changing cookieLength handling from a byte + cast to a direct int. This addresses a scenario where insufficient buffer validation could cause a panic. The Go vulnerability report (GO-2023-1534) explicitly lists this function as affected, and the patch directly targets this method. The combination of code analysis, commit context, and advisory references confirms this as the vulnerable function.