Fix Splode.Error.message/1

[jechol]

Contributor checklist

• [X] Bug fixes include regression tests
• [ ] Chores
• [ ] Documentation changes
• [ ] Features include unit/acceptance tests
• [ ] Refactoring
• [ ] Update dependencies

[zachdaniel]

I think we should do something like "if to string is implemented, to string, else inspect"

[jechol]

For example, when investigated using String.Chars.impl_for/1 both [] and [:a] return String.Chars.List, but while [] can be converted to a string using to_string, [:a] cannot. I think it's always better to use inspect for the following two reasons:

1. It is possible to use a try block to attempt to_string and fall back to inspect if it fails, but it feels a bit awkward.
2. It feels more consistent to always use inspect rather than having to_string and inspect separated based on the type.

I'm curious about your opinion.

[zachdaniel]

You're right :) I was thinking that this might somehow surface to end users, but that we don't use message/1 for displaying to the outside world.