Migrate to the latest version of the Engine API spec

[zah]

We need to review the recent changes introduced in the Engine API (one example is the inclusion of the safeBlockHash field in the fork-choice update call).

Some relevant spec PRs:
ethereum/consensus-specs#2851
ethereum/consensus-specs#2858
ethereum/consensus-specs#2876

[tersec]

I'm not sure if there's anything remaining to be done here:

• those are not engine API calls, but consensus spec changes
• set safe_block_hash to fork choice justified #4010 addresses Add safe_block_hash to notify_forkchoice_updated ethereum/consensus-specs#2851 and Bellatrix: pass justified as a safe block ethereum/consensus-specs#2858
• Fix param order in prepare_execution_payload ethereum/consensus-specs#2876 is part of an abstract aspect of the consensus spec, where it's not especially crucial it matches any particular implementation exactly, so long as it does handle the safe block hash properly
• update engine API spec ref URLs from alpha.9 to beta.1 #4030 does the minor update from the engine API (proper) alpha.9 to beta.1.

[zah]

Indeed, these improvements have been shipped in Nimbus v22.8.1