Support custom errors

[AuHau]

Thanks to Chronos v4 supports proper raises tracking, it now makes more sense to use exception tracking and specifically also custom errors to correctly signal error types.

I have a custom error type, that I have correctly added to raises and created for it specific Result type like this:

type
  SubscriptionError* = object of EthersError
  SubscriptionResult*[E] = Result[E, ref SubscriptionError]

When I used it with Questionable like this:

  proc onBlock(blckResult: SubscriptionResult[Block]) =
    without blck =? blckResult, err:
      raise err

Then I got an error from Nim that points out that the raised error is ref CatchableError type and not ref SubscriptionError. If I use the Result's API directly, then the expected error is correctly ref SubscriptionError