Function create_or_derive_api_key 

pub async fn create_or_derive_api_key(
    private_key: &EvmPrivateKey,
    nonce: u64,
    base_url: Option<&str>,
) -> Result<ApiCredentials>

Creates or derives API credentials using L1 (EIP-712) authentication.

First attempts POST /auth/api-key (create). On HTTP-level errors (e.g. nonce already used), falls back to GET /auth/derive-api-key (derive). Transport and network errors are propagated immediately without attempting the fallback.