Investigate configurability of devnet block time in `foc-devnet`

Previous attempts at trying to configurae the devnet block time resulted in burnt hands.

This requires changes on lotus, curio and synapse-sdk as well (I think). Although lower priority, configurability means that devnet can be spun up faster and worked with faster for devnet needs.

Start with the existing foc-devnet setup and trace how lotus, curio, and synapse-sdk participate in devnet block production. Review the prior configuration attempts and identify the integration points that prevent changing block time. Done means block time can be configured when launching the devnet and the faster setting works across the required components.

Written by the indexing model from the issue text.