Field "chain" is used twice with different meaning/definition

I would clarify what does "chain" mean, given that we have "parent.chain" that has a different definition.
Since the latter is dependent on / specific to this repository and doesn't have a correspondence on a on-chain value (EIPs are off-chain right?), I would consolidate to the former and make a clear definition of what is it.
There are irregularities currently on the "chain" field values, examples:

- Capitalized/UPPERCASE/lowercase (ETH/ETH vs Evmos/evmos)
- equal to the symbol of the native currency vs. to the name or shortname of the chain (ETH vs Solana vs evmos)
- is it a unique representation of the parent chain or parent native currency (by slip44 maybe?)? Seems so with children of Ethereum but not otherwise, like Aurora-NEAR, Avalanche-AVAX, etc..

In general, I would add comments to
https://github.com/ethereum-lists/chains/blob/master/model/src/main/kotlin/org/ethereum/lists/chains/model/Chain.kt
to help listers provide consistent values.