[io] Require static lifetime bound on Error

[Conaclos]

This PR requires types that implement embedded_io::Error to have a static lifetime.
This is a breaking change. However, this should not widely impact the ecosystem because most of the error types are static anyway.

Why this change?
This is basically the same rationales as d02f6db
Many crates require error types to implement core::error::Error and to be 'static.
One of the reason is because of core::error::Error::source that returns a dyn core::error::Error +'static.

Working with these crates and embedded-io makes things hard because you have to constraint the Error associated type on every generic functions.
Here is an example:

fn f<R: embedded_io::Read>(r: &mut R) -> Result<(), a_crate::Error<R::Error>>
where R::Error: 'static {}

Requiring 'static on embedded_io::Error makes things less tedious.
Moreover, it is considered as a best practice in the Rust community of requiring both core::error::Error and 'static on Error types.

I didn't make the change on other crates because their Error types don't implement core::error::Error (yet?).