miner: determine the ideal timeout for payload building

[calbera]

bera-geth/miner/payload_building.go

Lines 247 to 249 in cdd8fc2

	// TODO(Berachain): Using 4s for now to handle cases where block time exceeds 2s. To be
	// verified further after stable block time is in effect.
	endTimer := time.NewTimer(time.Second * 4)

With stable block time at 2s, determine the ideal timeout for building new payloads