Better error handling

[Alexangelj]

The contract has been reduced below the maximum contract size, which gives us room to improve the errors that portfolio can revert on. There's already an issue for reverting with custom errors instead of relying on solidity's native panic(uint) error codes (underflow/overflow), and we can further improve error handling by making sure no two errors are alike so its easier to find where they were thrown.

[Alexangelj]

Much better error handling in this release.