Review prepare next slot in gloas

we need to review how our `prepareNextSlot` timings work in gloas, especifically we need to check timings for
- when to run the scheduler, current 8 seconds in the slot, but I think it can be moved to 6 seconds because aggregation is done at that point `AGGREGATE_DUE_BPS_GLOAS = 5000`
- see when we sent FCU with payload attributes
- if we have the payload at 6 seconds when scheduler runs, sent it right away
- otherwise define some time (maybe 10 seconds, ptc deadline + 1 second to process it) to do payload attributes to build on EMPTY
- or as soon as we receive the payload based on `execution_payload` we can send the FCU with payload attrivbutes
- later once the PTC is more stable and all clients have it implemented, we can also include the PTC tiebreaker decision to reorg the payload and/or make a more informed decision on whether to build on FULL or EMPTY, ie. even if we have the payload we might wanna build on EMPTY if the PTC votes against the payload or it's DA being available