* Reduce duplication in error messages
This commit removes duplication in error messages where the same text
would show up multiple times in a fully rendered error message.
When using `derive(Error)` when the `#[from]` attribute is used there's
no need to also render that payload into the error string because the
`#[from]` establishes a "backtrace" which means that when the full
context of an error is rendered it will include the `#[from]` in the
lower frames of the backtrace anyway.
This commit audits the `derive(Error)` implementations to avoid
duplication in the rendered error messages, ensuring that if `#[from]`
is used then the `#[from]` field isn't also rendered in the textual
description.
* Search the full error in wast assertions
Don't just search the top error, but search the whole backtrace by using
the `{:?}` format instead of `{}`.
