Engine API getPayload handlers don't check for too-new forks

[tersec]

It does check

nimbus-eth1/nimbus/beacon/api_handler/api_getpayload.nim

Lines 63 to 66 in d814d84

	let payload = payloadGeneric.V3
	let com = ben.com
	if not com.isCancunOrLater(ethTime payload.timestamp):
	raise unsupportedFork("payload timestamp is less than Cancun activation")

nimbus-eth1/nimbus/beacon/api_handler/api_getpayload.nim

Lines 91 to 94 in d814d84

	let payload = payloadGeneric.V4
	let com = ben.com
	if not com.isPragueOrLater(ethTime payload.timestamp):
	raise unsupportedFork("payload timestamp is less than Prague activation")

i.e. whether one tries to send an engine_newPayloadV3 with a payload from before Cancun starts, or engine_newPayloadV4 with a payload from before Prague begins, but it does not check whether one sends an engine_newPayloadV3 with payload with a timestamp within Prague.

https://github.com/ethereum/execution-apis/blob/v1.0.0-beta.4/src/engine/cancun.md#update-the-methods-of-previous-forks states:

For the following methods:

• engine_forkchoiceUpdatedV2
• engine_newPayloadV2
• engine_getPayloadV2

a validation MUST be added:

1. Client software MUST return -38005: Unsupported fork error if the timestamp of payload or payloadAttributes greater or equal to the Cancun activation timestamp.

and similarly
https://github.com/ethereum/execution-apis/blob/v1.0.0-beta.4/src/engine/prague.md#update-the-methods-of-previous-forks states:

For the following methods:

• engine_newPayloadV3
• engine_getPayloadV3

a validation MUST be added:

1. Client software MUST return -38005: Unsupported fork error if the timestamp of payload or payloadAttributes greater or equal to the Prague activation timestamp.