ethrex: update guest client, support risc0, and run more complete integration tests

[jsign]

This PR:

• Updates Ethrex to their latest commit in main. (Note, they didn't merge the Risc0 trie usage yet -- so in the near term I'll update again when that is merged).
• Their chain config struct changed a bit, so while fixing it I refactored things a bit in the conversion logic.
• Enabled Risc0 using the unaligned feature from rykv.
• Added mainnet_blocks and invalid_blocks for Ethrex in the tests crate.
• Now that they're available, also run them in CI since they were skipped. Running time looks acceptable.

I wanted to push further to add ZisK, but there is a pending PR in Ethrex to switch from secp256k1 (which ZisK doesn't support) to k256, which should solve the problem. So for ZisK integration, we'll have to wait for that PR to be merged.

Fixes #163
Fixes #161