rpcdaemon: update JSON-RPC spec to fork 0502b44

[canepat]

Recently, we cloned official Ethereum JSON-RPC Execution API repository into our fork in order to:

• experimenting in using and maybe customising the official spec for our validation needs
• adding the metadata specification for missing namespaces (e.g. debug, trace, ots)
• hopefully being able to contribute back some of our changes after experimentation

This PR updates our copy of the full specification to the version generated from erigontech/execution-apis@0502b44, which is equivalent to the official erigontech/execution-apis@3ae3d29 plus the following changes:

1. fixes in eth_getStorageAt Fix eth_getStorageAt and uint256 definitions ethereum/execution-apis#509
2. fixes in engine_forkchoiceUpdated, which we previously applied directly to the generated our copy of the full spec rpcdaemon: fix Engine API V3 in JSON-RPC spec #1924

Next Step
The next step will be a fully automated solution including our fork as Silkworm submodule (branch main_silkworm) and thus generating the full specification at build time.

Extras

• fix null validation in our json_rpc::JsonRpcValidator
• make unit tests more strict by checking also the validation errors
• slightly improve comment in conan.cmake