Add comments explaining when our client is used instead of the rollup stack's client

[samlaf]

We have a client in the repo: https://github.com/Layr-Labs/eigenda-proxy/blob/feat--openapi-spec/client/client.go

Seems it's only used for simple commitments, meaning nitro doesn't have a client the same way op does?

Could we document this in the code, as comments above the client struct? And link to the op client, explaining why we only have a client for the simple commitment mode.

[samlaf]

Related to this, it seems like we use a query parameter of ?commitment_mode=simple to send simple commitments.
Could we change this to be in the path instead? like GET /get/simple/{hexEncodedCommitment}? Would greatly simplify the logic around here in the code.