[SamAg19]

Issue Addressed

Introduces REST-SSZ wire types required for the REST-SSZ engine API implementation based on the spec

Proposed Changes

PR #9652 has the complete implementation of the REST-SSZ engine API and support uptil Gloas but since the diff is 6k+, reviewing such a PR will not be possible and hence I will be creating multiple smaller PRs from PR #9652 as mentioned in this comment to improve reviewability starting with the following PR of adding REST-SSZ wire types.

• Introduces ssz_structures.rs which holds the wire containers required for the REST-SSZ engine along with the conversions between those containers and the internal SSZ containers.
• Derives Encode and Decode on existing types that can be reused instead of redeclaring them in ssz_structures.rs
• Adding MaxExecutionRequestsPerPayload, MaxErrorBytes and MaxVersionedHashesPerRequest types to the EthSpec trait in accordance with the spec

[SamAg19]

@macladson Updated the branch to incorporate PR #10378 fixes that addresses the cargo-audit in the check-code CI run. Everything should pass now.