Support crate for `eth`: `no_std` Ethereum verification boundaries.
Most users should depend on the facade crate instead:
```toml
[dependencies]
eth = "0.4"
```
Crates.io: <https://crates.io/crates/eth>
This package is published separately so the `eth` workspace can keep small,
auditable crate boundaries. Treat it as a lower-level building block unless the
`eth` documentation explicitly says otherwise.