Sqlite: impl Encode/Decode for Url

[braddunbar]

I'd like to use a Url as a Sqlite column. This allows it!

Does your PR solve an issue?

Nope.

Is this a breaking change?

This will cause code that previously attempted to derive FromRow with a Url field to compile now when it didn't before. I wouldn't classify this as a breaking change.

[abonander]

This is what the Text adapter was designed for: https://docs.rs/sqlx/latest/sqlx/types/struct.Text.html

It doesn't make sense to support Url directly as a type because it doesn't map to a native SQLite datatype (not even remotely like the date-time types do).