ether.js v6 migration

[anajuliabit]

Remediate #678

[anajuliabit]

@zajck good catches, I applied all!

[coveralls]

coverage: 99.702% (-0.03%) from 99.733% when pulling 353cb4d on etherv6_migration into ab3d4ba on main.

[zajck]

And a few things that I couldn't comment directly:

• There's another case of toHexString
  

  boson-protocol-contracts/test/util/utils.js

  Line 271 in e8a4973

  const pBuffer = Buffer.from(slot.toHexString().slice(2), "hex");

• in test/util/upgrade.js, we have BigInt.toNumber() in some places and it should be changed to Number(BigInt). This happens on lines 470, 523, 539, 540, 620, 1236*, 1365*, 1392*, 1679, 1733. In those marked with * you can probably even get rid of all casting and just assign store to variable whatever getStorageAt returns

I guess these are my last requests. If we miss something in the upgrade test files, I'll find it anyway when I merge this into upgrade tests.

[zajck]

looks good 👍

[mischat]

:)