feat: impl From<ExpectedNumber> for RichPattern

[seftontycho]

Currently it is not possible to use the number::Number parsers with the Rich error type as RichPattern does not implement From<ExpectedNumber>.

This PR adds the missing impl in the number module so it is appropriatley feature gated.

Not previously possible:

fn parse_u8<'a>() -> impl Parser<'a, &'a str, u8, extra::Err<Rich<'a, char>>> {
    let u8_num: Number<STANDARD, &'a str, u8, ErrRich<'a>> = number();
    u8_num
}

[seftontycho]

I'm not exactly sure what variant of RichPattern to use here, Label seemed the most fitting but then I'm not sure on the label name.

Open to suggestions better than "number".

[zesterer]

Thanks! I think adding a new variant to RichPattern is fine also, and might be worth it for the ability to disambiguate at a type level (we don't want end users pattern-matching on strings, if we can help it). If you could, also added #[non_exhaustive] to the enum would also be great. It's a breaking change, but there are already several of those lined up anyway!

[seftontycho]

Thanks! I think adding a new variant to RichPattern is fine also...

How would you like that to work feature wise? If we added RichPattern::Number it wouldn't really make sense if a user wasn't using the lexical-numbers feature.

[zesterer]

Apologies, GitHub swallowed the notification for this.

I think the only change needed is to add #[non_exhaustive] to the RichPattern enum.