fix: NetworkVariable LastUpdateSent client timing

[NoelStephensUnity]

Fixing a possible scenario where a client could have a NetworkVariableBase.LastUpdateSent value that was incorrect. This just uses the synchronized ServerTime to assure the LastUpdateSent is always less than the current ServerTime.

Changelog

• Fixed: Issue where clients could have a wrong time delta on NetworkVariableBase which could prevent from sending delta state updates.

Testing and Documentation

• No tests have been added.
• No documentation changes or additions were necessary.