meta(`anvil`): make `anvil` a `reth` extension / sparse client

### Component

Anvil

### Describe the feature you would like

`anvil` and `reth` should be best friends.

It makes sense to do this. It would make anvil more accurately produce EL client behavior because *it is* an EL client.

### 'sparse' client

A 'sparse' client would be like a reduced functionality client with certain checks disabled (like connecting to a beacon client, etc.). I would think this may be useful for reth testing in CI as well, maybe.

The reth_anvil client should support extensions. This does make sense w.r.t. custom RPC methods, as it would make extending custom methods much easier. Hot loading such modules would be *very* intriguing.

### Additional context

Inshallah, we get this sooner than we got v1.0.0 foundry