include z difference in fence test

[uwer]

Setting a fence or roaming fence follows the syntax of
NEARBY FENCE ROAM

In The test for nearby matches (fence and roaming fences) tests for group, id an distance
internal/server/fence.go#L367

Describe the solution you'd like
I propose to add an optional additional argument to the original statement to allow z-value difference
NEARBY FENCE ROAM

Once the value is fed through simple test in
internal/server/fence.go#L402C5-L402C5 would do the trick

this would allow for potential assignment of timestamp values as Z values of a point and reducing the match within a fence to be also within a reasonable time window

Describe alternatives you've considered
this would potentially be possible to use a whereeval clause based on the z value or a field ts by
creating a boolean test as (not the correct syntax);
"return abs(FIELDS.ts - ts ) < ts difference>"