op-challenger: Add subcommand to check sufficient state history is available

Add a subcommand to `op-challenger` that checks that state history is available from a supplied L2 EL and rollup node (op-node). The node requires history at least as far back as the `--game-window`.

Suggest we check the EL by calling `eth_getProof` for something like the withdrawal root at a block at the start of the game window.
For the rollup node, check by calling `optimism_safeHeadAtL1Block` with a L1 block number that occurred at the start of the game window.

Start by locating the existing op-challenger subcommands and the handling of --game-window. Trace how the command can reach the L2 EL and rollup node, then investigate eth_getProof and optimism_safeHeadAtL1Block at the game-window boundary. Done means the subcommand reports whether both nodes retain sufficient history.

Written by the indexing model from the issue text.