Fix arithmetic overflow error in 'accountsHash' function

[Robin-3]

I noticed an arithmetic overflow error in the 'accountsHash' function located in the file "src/day4/Account.mo". The error is causing the program to throw an 'arithmetic overflow' with error code IC0503.

I have identified the problematic code block. Here's the corrected code:

  public func accountsHash(lhs : Account) : Nat32 {
    let lhsSubaccount : Subaccount = Option.get<Subaccount>(
      lhs.subaccount,
      _getDefaultSubaccount(),
    );
    let hashSum = Nat.add(
      Nat32.toNat(Principal.hash(lhs.owner)),
      Nat32.toNat(Blob.hash(lhsSubaccount)),
    );
    Nat32.fromNat(hashSum % (2 ** 32 - 1));
  };