Cleanup of legacy tooling in smart-contracts tests

[clemsos]

We still have legacy tools in our smart contracts test suite that should be removed to make everything more consistent and maintainable

• tests using truffle
• bignumber.js
• move to ES6 import pattern ES6 import for smart contracts tests #10827

[clemsos]

Regarding outdated Truffle patterns, the major changes are:

• artifacts.require replaced by ethers.getContractFactory
• ˋaccounts addresses replaced by ˋethers.getSigners
• use the ethers signers with ˋconnect() instead of passing ˋfrom in functions calls
• replace instances of ˋbignumber.jslib by ethersBigNumber`. We introduced helpers to facilitate bn comparisons in chore(smart-contracts): remove chai + bignumber pattern from tests #12851

Some examples of such changes are demonstrated in #12699

[clemsos]

see also errors for ethers v6 for context

[clemsos]

done in #13365