add --contender.arg flag

[zeroXbrock]

adds a new flag --contender.arg, which may be specified multiple times, that passes arbitrary args to contender, complete with default values and the ability to override them, as well as passing additional args.

example:

go run main.go cook l1 --contender --contender.arg "--tps 100" --contender.arg "-a 20"

to see that this is working, run docker ps, get the container ID of contender, then run docker logs $CONTAINER_ID. You should see 21 accounts getting funded (the default account always gets funded, maybe should fix), and 100 txs being sent. Something like this:

$ docker logs ffdd2bc90da3
2025-08-13T00:08:40.961364Z  INFO contender: 83: generating seed file at /root/.contender/seed
2025-08-13T00:08:40.986774Z  INFO contender::default_scenarios::fill_block: 57: Attempting to fill blocks with 36000000 gas; sending 100 txs, each with gas limit 360000.
2025-08-13T00:08:40.986788Z  INFO contender::commands::spam: 139: Initializing spammer...
2025-08-13T00:08:41.009647Z  WARN contender::util::utils: 127: No private keys provided. Using default private keys.
2025-08-13T00:08:41.014946Z  INFO contender::util::utils: 292: sending funding txs (21 accounts)...
2025-08-13T00:08:41.015161Z  INFO contender::util::utils: 329: waiting for funding tasks to finish...

note: you can also pass positional args, which enables you to run builtin scenarios, and pass them args if needed:

# run the builtin "storage" scenario, which fills lots of storage slots
go run main.go cook opstack --contender --contender.arg "--tps 40" --contender.arg "storage"

# write to 5000 slots (instead of the default 500)
go run main.go cook opstack --contender --contender.arg "--tps 40" \
--contender.arg "storage" --contender.arg "-s 5000"