refactor(l2): remove the dev_mode CLI option and infer dev mode from on‑chain proof getters

[julienbrs]

Motivation

“dev mode” is now simply the case where the on‑chain proposer contract returns only the DEV_MODE_ADDRESS for all proof getters, in which case we fall back to the Exec prover. Removing the CLI option shifts the truth to on‑chain configuration.

Description

• Remove the dev_mode field from all L2 CLI structs and configs.
• Delete all code paths that branched on the old flag.
• Update get_needed_proof_types to always call the on‑chain getters for every ProverType and collect those whose addresses differ from DEV_MODE_ADDRESS. If the resulting list is empty, return vec![ProverType::Exec] as the implicit dev‑mode fallback.

Closes #3698

[avilagaston9]

Hi @julienbrs!
Thanks for the contribution, and sorry for the delay in reviewing it. I've left one comment that needs to be addressed.

[julienbrs]

Thanks for the review @avilagaston9, I’ve restored the original variable names, should be good now

[avilagaston9]

Let's remove ETHREX_PROOF_COORDINATOR_DEV_MODE from the entire codebase, including all places where it is set, as well as from the documentation.