Do not model an insufficient bid with cvm.error

[symbiont-eric-torreborre]

I think we should leave cvm.error to real errors where a contract don't know how to make further progress. For example here:

@executable
def _bid(id: Identifier, amount: int) -> Optional[Bid]:
    row = get_auction(id)
    if isinstance(row, None):
        cvm.error(f"You don't have access to this auction.")

However when someone places a bid with an insufficient amount:

if amount <= last_bid.amount:
        cvm.error(f"The bid amount must be larger than current bid amount ${last_bid.amount}.")

This is expected behaviour and we should return a job complete result indicating that the bid was insufficient.

The downside of using cvm.error everywhere is that we end-up creating job fail events which are indistinguishable from job fail events due to a channel which cannot be rotated (because the key alias is not the owner anymore), a temporary failure to post a transaction to Smartlog or a bug on the platform.

Maybe one way forward is to make a stronger distinction in the language between failures and errors where

• failures are non-"happy path" conditions but totally expected flows
• errors are the equivalent of asserts in other programming languages