Implement Display for LocatedSpanEx

[ebkalderon]

Changed

• Replace explicit ToString implementation for LocatedSpanEx with Display.

This should make nom_locate more ergonomic to use with Criterion. Note that the type annotation T is constrained here by ToString instead of Display so we can support Display for LocatedSpanEx even for types that do not implement Display, but do implement ToString.

Fixes #39.

[progval]

This adds two extra copies when using ToString. Do you know if they get optimized out?

[ebkalderon]

@progval Hard to say. There are exactly two occurrences of memcpy in both versions, according to Compiler Explorer, with most of the assembly differences being the addition of the generated std::fmt symbol boilerplate. No additional calls appear to have been introduced, AFAICT. Perhaps you might be able to spot a meaningful difference?

[progval]

Perfect, thanks!