docs: repoint the NetworkTimeSystem API cross-reference at the new namespace

xref targets are fully qualified UIDs, so the one in networktime-ticks.md stopped resolving when the
type moved. DocFX renders an unresolved xref as its raw text, which reads as a broken link on the
published page rather than failing anything in this repo - there is no docfx job here.

Nothing else in Documentation~ needs changing. Every code sample that touches these types reaches
them through NetworkManager (LocalTime.TimeAsFloat, NetworkTickSystem.Tick), which never names the
type and is unaffected; the remaining mentions are prose or links to this same page. The old names in
apiupdaterproject/README.md and the CHANGELOG are the 2.x side of before/after tables and are correct
as they stand.

No upgrade note added. The samples on that page do not need the new import, so a note about it would
be advice for a reader the page does not have, and the landed editor relocation set the precedent of
updating the affected sample without prose. The CHANGELOG entry covers the move.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Documentation~/advanced-topics/networktime-ticks.md

@@ -183,6 +183,6 @@ For games with short play sessions casting the time to float is safe or `TimeAsF
 > [!NOTE]
 > The properties of the `NetworkTimeSystem` should be left untouched on the server/host. Changing the values on the client is sufficient to change the behavior of the time system.
 
-The way network time gets calculated can be configured in the `NetworkTimeSystem` if needed. Refer to the [API docs](xref:Unity.Netcode.NetworkTimeSystem) for information about the properties which can be modified. All properties can be safely adjusted at runtime. For instance, buffer values can be increased for a player with a bad connection.
+The way network time gets calculated can be configured in the `NetworkTimeSystem` if needed. Refer to the [API docs](xref:Unity.Netcode.GameObjects.Timing.NetworkTimeSystem) for information about the properties which can be modified. All properties can be safely adjusted at runtime. For instance, buffer values can be increased for a player with a bad connection.
 
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