Added type description to errors when using --arg

[waldmatias]

What

Adding what type (Symbol, Byte, etc) a specified argument via the --arg option is trying to be parsed into, and if a parsing error occurs, include it in the error output to provide a hint as to why the arg is unable to be parsed.

Why

Currently, there's a very general and unhelpful error if an error occurs when parsing a val to type.

Known limitations

A simple change, basically to show more error information when specifing --arg.

[leighmcculloch]

This is great 👏🏻, and really improves the experience of interacting with args. Great idea.

There's one thing we can do to possibly further improve the output that I note below, but I think this already goes a long way to improve the situation, so we could merge this as is and consider follow ups to continue to improve.