accurately display L2/L3 status

[tessr]

Right now, all chains are listed as L2s. This value is hardcoded into the generated files. However, we should accurately reflect whether a chain is an L2 or L3, and for L3s display their parent chain.

Constraints

We don’t want to introduce the concept of “new Superchains” within the Registry. Although there is the concept of separate Superchains (e.g. Sepolia vs mainnet) today, an L3 on Base is still part of the same Superchain as Base or OP Mainnet. (And from a marcomms perspective, there’s really only one Superchain anyways.)

Proposed Solution

Don’t enshrine L3 status in the directory structure, since this implies that these are separate Superchains. Rather, include a parent chain / layer

The information in the generated files is quite a nice and accurate way to describe this, I think:

    "parent": {
      "type": "L2",
      "chain": "mainnet"
    }

[geoknee]

As discussed in slack, we feel it would be better to place L3s in a subdirectory named after their parent chain. The folder hierarchy then represents the parent/child relationship between chains.

We should consider renaming "superchain target" to "parent chain", and updating instructions on how to add a new directory for L2s with L3 children (or LNs with LN+1 children). We also need to update the bindings to traverse deeper into the directory tree to load all of the chains.