fix: derive job deadline from attributes timestamp

[mattsse]

ref #5623

previously we were setting a fixed 12s timeout for payload building jobs

however according to the spec:

https://github.com/ethereum/execution-apis/blob/main/src/engine/paris.md#payload-building

Client software SHOULD stop the updating process when either a call to engine_getPayload with the build process's payloadId is made or SECONDS_PER_SLOT (12s in the Mainnet configuration) have passed since the point in time identified by the timestamp parameter.

This sets the deadline as (attributes.timestamp - now) + 12s

[rkrasiuk]

lgtm