[reginaldalfret]

Purpose of this PR

Fixes #4249.

Under packet loss, TimeSyncMessage was sent reliably using NetworkDelivery.ReliableFragmentedSequenced because k_SkipMessageTypes omitted NetworkMessageTypes.TimeSync (despite the code summary explicitly stating it should be skipped due to always using unreliable delivery). Consequently, delayed retransmitted time sync messages caused the client clock to hard-reset backwards when passing HardResetThresholdSec, causing owned NetworkTransforms to stall until the clock caught up.

This PR:

1. Adds NetworkMessageTypes.TimeSync to k_SkipMessageTypes and explicitly registers it as NetworkDelivery.UnreliableSequenced in MessageDelivery.UpdateMessageTypes().
2. Updates MessageDelivery.GetDelivery lookups to resolve mapped delivery types cleanly.
3. Guards TimeSyncMessage.Handle against applying stale out-of-order time sync messages.
4. Adds regression unit tests in MessageRegistrationTests.cs.
5. Updates CHANGELOG.md.

Changelog

• Fixed: Fixed an issue where TimeSyncMessage was sent using reliable delivery, which could cause delayed packets under packet loss to reset client clocks backwards and stall NetworkTransforms. (TimeSyncMessage is sent reliably, so a late one resets the client clock backwards and stalls its NetworkTransforms #4249)

Documentation

• No documentation changes or additions were necessary.

Testing & QA

Automated tests:

• Covered by new automated tests (WhenCheckingTimeSyncMessageDelivery_UsesUnreliableSequencedDelivery, WhenCheckingTimeSyncMessageDeliveryType_UsesUnreliableSequencedDelivery)

[cla-assistant-unity]

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