Implement `core::error::Error`

[michael-p]

Hey, thanks for your work on this nice library!
I think it would be great if the main error type of the crate would implement core::error::Error, thus making it easier to interoperate with other libraries in the ecosystem. However, this would increase the MSRV to 1.81, and also might pull in some of the formatting machinery in core::fmt.
If you are open to this I can send in a PR.

[thejpster]

That's a little high for my tastes. Could you put it behind a feature gate?

[michael-p]

Sure - opened #180 for further discussions!