chore: do validation checks before processing the packet in 04 channel v2

[gjermundgaraba]

Description

closes: #7636

It was also mentioned during the audit that this should also be done for timeout, but I guess the moving the Route loop earlier would make trouble in the no-op case? If there are some other cases here I should cover, let me know and I will add it to the PR.

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[sonarqubecloud]

Quality Gate failed for 'ibc-go'

Failed conditions
66.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud

[DimitrisJim]

I don't see any validation in TimeoutPacket that can be moved before core handler is actually called.