refactor(sequencer): clarify transaction cost estimation

[ethanoroshiba]

Summary

Refactored calculation of total transfers made in a transaction to helper function for clarity.

Background

See here: #1905 (review)

I think we should remove this function entirely in favor of two functions, calculate_fees_for_transaction (already exists) and calculate_funds_moved_by_transaction (essentially move the loop over the actions to it). The check for enough funds would then take the result of both methods.

Changes

• Moved calculation of all transfers made in a transaction to helper function, and called this helper function in get_total_transaction_cost().

Testing

Passing all tests, no additional tests needed.

Changelogs

No updates required.

Related Issues

closes #1907