Add comments why `unprefixedHexToBytes` or `bytesToUnprefixedHex` is used

[jochem-brouwer]

In some places in the monorepo we use unprefixedHexToBytes or bytesToUnprefixedHex. Those are methods from util which are marked as deprecated. We still use those in certain places with in most/all cases an optimization argument. We should review where these deprecated are used, and if there are still arguments why we should keep using those, we should explicitly comment why this is used such that we dont accidentally change this.

Will assign myself here, I think most of them were left as using the deprecated variant once we changed using those utilities from ethereum-cryptography to using our own exported variants from @ethereumjs/util