simulators/ethereum/engine: Add newPayload while syncing tests to increase coverage

[marioevz]

Adds several test cases for valid and invalid payloads while the client is in SYNCING state to increase tests coverage.
All Invalid * NewPayload test cases now have a (Syncing) variant which adds the following steps:

• The main client is put into SYNCING state by being disconnected from the CL Mocker, producing a new payload which is not sent to the client, and sending a fcU(head -> missingPayload)
• The client is sent a newPayload(alteredPayload), where alteredPayload.parent==missingPayload, and has incorrect stateRoot, or incorrect gasLimit, etc, but the hash of this payload is correctly calculated.
• The test expects an ACCEPTED or SYNCING status response from the newPayload
• The client is then revealed the missing payload via newPayload(missingPayload), which shall return VALID
• newPayload(alteredPayload) is sent again and the expected response is now INVALID
• Client Eth JSON-RPC is queried eth_getBlockByHash(alteredPayload), which shall return an error

Similar test case Valid NewPayload->ForkchoiceUpdated on Syncing Client is added which follows the same steps but using a valid payload.

Geth is having an unexpected behavior with test case Invalid Number NewPayload (Syncing):

• alteredPayload has alteredPayload.parent==missingPayload but also alteredPayload.Number==missingPayload.Number
• After newPayload(missingPayload), newPayload(alteredPayload) sends client into SYNCING mode instead of returning INVALID.

Nethermind is passing all new tests.

cc @mkalinin @MariusVanDerWijden