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 1M transactions to the parachain zombienet network and check if all transactions are getting finalized
• check the limits on long term run,
• check how blocks are filled,
• check if invalid transactions are rejected,
• check time-to-event (e.g. in block, finalized, invalid), to see if we have some regression,
• send different transactions - heavy and light,
• send future and then ready, see if all gets finalized (fatxpool: add heavy load tests based on zombienet #7257),
• check mortal transactions (shoud be done in fatxpool: cross check (and improve) support for mortal transactions #5626),
• check submit and submit_and_watch,
• 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 fatxpool: 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/).

[iulianbarbu]

Another update (hoping these are useful, considering we're working on this for some time):

1. ttxt is shaped into a lib here: Enabled ttxt as a lib michalkucharczyk/tx-test-tool#22
2. ttxt is being used as a lib in here: fatxpool: add heavy load tests based on zombienet #7257 - work in progress, until we settle on ttxt usage as a lib, but I'll ask @michalkucharczyk for a review over this as soon as I am confident the work with the testing scenario is done.
3. Working on the last bits of the scenario described here: fatxpool: add heavy load tests based on zombienet #7257 (comment). The scenario runs fine, it is just that I would like to assert on expected account nonces for the accounts under test, after the test finishes. There might be an easier route by checking how many txs have been finalized (ttxt reports a summary where it gives this number, and we can reuse it - but I need to see how I can expose that via API)