Clear _currentSwapTokensOut and _currentSwapTokensIn every each operations in BatchRouter

[elshan-eth]

Description

This PR fixed a problem with _currentSwapTokensIn/_currentSwapTokensOut token sets in BatchRouter. We cleared only _currentSwapTokenInAmounts, _currentSwapTokenOutAmounts, and _settledTokenAmounts at the end of the operation but didn't do it for _currentSwapTokensOut/_currentSwapTokensIn. This problem happens every time we have multiple operations in one transaction.

In the first iteration, I tried to create an index for all mappings which we iterate each operation. It means that if the index changes, we don't need to clear every property. This way had a problem with stack too deep (without viaIR compilation) and gas was increased.

This way is simple and cheap.

NOTE: merge this PR after #731

Type of change

• [ ] Bug fix
• [ ] New feature
• [ ] Breaking change
• [ ] Dependency changes
• [ ] Code refactor / cleanup
• [ ] Documentation or wording changes
• [X] Other

Checklist:

• [ ] The diff is legible and has no extraneous changes
• [ ] Complex code has been commented, including external interfaces
• [ ] Tests have 100% code coverage
• [ ] The base branch is either main, or there's a description of how to merge

Issue Resolution

Closes #707

[elshan-eth]

The code seems nice, but just a question: If amounts is cleared and the amount of token to transfer is 0, why do we need to clear tokensIn and tokensOut, if effectively that token won't be transferred? I mean, looks like we added at least 1k gas to do this. Isn't it better to check if amount is greater than 0 before transfering the asset from/to the user during settle?

if there will be several calls within 1 transaction (I don’t know if this makes sense), it would be the same. I mean we can remove elements and it will cost around 100 gas but also if we don't remove this the next call will read it to compare it with zero and also pay 100 gas more.