automatically expirable character variables

[TeoTwawki]

There was a private discussion recently that called back to prior discussions about this subject, during the most recent discussions consensus strongly leaned into a new table row containing a unix time stamp. If non zero, this field would be the date to automatically remove the variable on map startup -and- on read attempt.

Existing character variable behavior would be fully retained. Existing variables are delete when SET with a value of zero, and non-existing ones return zero when checked. We must not change that - everything would break.

The new timestamp field would be treated similarly: 0 means we do not attempt to auto expire, non existing vars treat as 0. Existing calls to set a character variable would not need any updates.

It was suggested that while adding a new param onto the existing character variable functions is trivial using a new function/bind name may be for the best to avoid confusion. perhaps player:setExpiringCharVar("name", value, timestamp)" and a corresponding get that returns the timestamp if not both the value and timestamp together. New name or not can be debated further if need be.

We didn't discuss it, but I think we could do with doing the same thing to server variables.

Alt forms decided against (for documentation purposes):

• Keeping timestamp is the value but assigning a "type" as a 3rd value, where type 1 would be "this is a timestamp, expire it". This was deemed less useful that having the option to still have the value in the future.
• Using a separate table to store time stampy type things instead of storing them as character variables. This was deemed unnecessary.

[TeoTwawki]

This feature was implemented in #4437