Add new image type and update dependencies.

[LacticWhale]

In current state, specific manga site started to use webp frequently, which resulted in exceptions on almost every request.

feat: add WebP type
feat: expose mappers
chore: update dependencies

Not mentioned in the commit description, but with new version of dart_mappable, all classes now have copy method. (previusly there was an issue with Image class and it's children)

All changes tested.

[LacticWhale]

I don't really know about package version but we actually might want to bump minor version e.g. 1.1.0