Do not use throw on happy path

Currently, it seems that at ParsableArgumentsValidation.swift:140, there is a `throw ValidationResult.success` that triggers on the regular happy path. This makes it very annoying to debug your code if you use a Swift error breakpoint in Xcode, as it will trigger several times before getting to the actual code that needs debugging.

I think most Swift code generally avoids throwing for program flow, and it would be nice if this code could also be changed to avoid that, to make debugging easier.

Start in ParsableArgumentsValidation.swift at line 140 and trace how the successful validation result is propagated through the surrounding flow. Determine how to avoid throwing on the happy path while preserving validation behavior, then verify that Swift error breakpoints no longer stop on successful validation.

Written by the indexing model from the issue text.