fatxpool: add heavy load testsuits

[michalkucharczyk]

There should be some mid/long term tests that are not intended to be executed during CI, but could be executed locally by a developer or by the QA team during the release process.
Some ideas for testing:

• send future and then ready, see if all gets finalized,
• check mortal transactions,
• check if invalid transactions are rejected,
• check time-to-event (e.g. in block, finalized, invalid), to see if we have some regression,
• send 1M transactions to the parachain zombienet network,
• check how blocks are filled,
• check if all transactions are getting finalized,
• check submit and submit_and_watch,
• check the limits on long term run,
• send different transactions - heavy and light,
• make sure nodes are not getting disconnected.

Those should be executed in local zombienet network, possibly in different configurations (e.g. one collator, rpc + collator, rpc + 3x collators).

[iulianbarbu]

Small update on this - I transformed the zn DSL files from #7100 into zombienet-sdk files: #7257. Most of them are using the same zombienet network: two relaychain validators with one parachain collator/validator, or three collators (where two of them are validators), or four collators (where three of them are validators).

The distinctive parts for these networks are the chain specs used for the parachains, and the arguments passed to each collator node, which are the same for the collators of the same network, but vary slightly between collators of different networks, as expected. My thinking though is that some args might need to be modified/removed/added to the base argument list, if these base networks will be used for further local testing, manually (possibly the chainspecs can be slightly updated/modified too). The ways this can be achieved is:

• modifying the test file locally, and rerunning the test (which implies its recompilation)
• extracting the zombienet infra written for fork-aware-tx-pool: add heavy load tests based on zombienet #7257 and use it in a CLI which would allow spawning of these regular networks, with small tweaks, and making clear where their base dirs can be found for logs retrieval or any other information dump related to tests (since this CLI might be integrated with https://github.com/michalkucharczyk/tx-test-tool/).