Add a flag to generate zkApp transactions with several account updates

The `update-state` subcommand of the zkApp test transaction tool now accepts `--num-account-updates`, which repeats the update against the zkApp account within a single transaction. This raises the cost of the generated transaction towards the network's per-transaction zkApp limit, which is useful for load-testing archive nodes and for checking how expensive transactions are handled.

Because events and actions are attached to every account update, the tool now counts them across all updates when checking the network's event and action limits, and reports the total if the limit would be exceeded.
