proposer: Use batch RPCs to build game state

The kona-sp1-proposer issues dozens of RPCs in sequence to generate state. Assume 10-100ms per RPC, it can take several minutes to build the game state, thus inflating the time to respond to games.

Start at the kona-sp1-proposer entry point and trace how it currently issues RPCs while generating game state. Identify the sequential RPC calls and determine how batch requests should replace them; done means game state is still generated correctly with fewer RPC round trips and a shorter response time.

Written by the indexing model from the issue text.