Convert RpcBlock to an enum that indicates availability

[eserilev]

Issue Addressed

In block lookup an RpcBlock is maybe available. In Range sync and backfill sync the RpcBlock is guaranteed to be available because consistency checks are made before the RpcBlock is constructed. In downstream code when we process blocks from lookup and sync, we are treating the RpcBlock as maybe available which adds match statements and edge cases that are mostly irrelevant for sync.

Proposed Changes

This PR is a first step towards cleaning up block processing. RpcBlock is now an enum with Available and MaybeAvailable variants. These variants are constructed when appropriate.

Additionally the RpcBlockInner is created based on the blocks fork variant. i.e. Deneb or Electra blocks will always use theRpcInnerBlock::BlockAndBlobs variant, even if blobs for that block don't exist (or may not be available yet)

In a subsequent PR, I'll be updating the block processing code paths to remove availability checks for the RpcBlock::Available variant. In the interest of keeping these PR reviews manageable this PR sticks to just converting the RpcBlock to an enum

[mergify]

Some required checks have failed. Could you please take a look @eserilev? 🙏

[eserilev]

need to fix a few tests but the general idea is here