Set TxType for scenario txs

[zzzzzzch]

Hi, this is a great perf tool. I found that spammer sends EIP-1559 txs by default, which is fine, but sometimes eth-forked/custom node clients may not support EIP-1559 and therefore it is needed to be specified to send legacy txs.
So this PR adds the legacy option to specify sending legacy txs.

please review and feel free to comment.

[zeroXbrock]

hey @zzzzzzch thanks for the PR! Sorry it took me so long to get back to you -- I recently did a bunch of refactoring and wasn't sure how this would fit until later.

This is a good idea, but I think it would be even better if instead of a boolean for legacy, we had an enum to support many tx types. That way, we don't have to add additional params later on; just more enum values.

The codebase has been shuffled around quite a bit since you pushed this so you might want to start this on a fresh branch and cherry-pick the code you need from this PR, but it's up to you :) Looking forward to your next commits!

[zzzzzzch]

finally found some time to refactor this PR, and apologize for the delay. I noticed there's also a recent PR #115 supporting 4844, and I referenced some comments from that PR during the refactoring.
Currently, there are still some tests that need to be fixed, I'm working on this.
please review and feel free to comment.

[zzzzzzch]

all work is done, and some code changes such as type definitions are similar to PR #115. Therefore one of the two PRs will need to be rebased onto the other before making further changes.
please review and feel free to comment

[zeroXbrock]

Thanks for the updates! I like the design, just had a few minor concerns.

[zeroXbrock]

thanks @zzzzzzch !!