EnumIs: Allow custom variant function names

[Mange]

I have an enum that basically looks like this:

#[derive(EnumIs)]
enum Value {
  U8(u8),
  String(String),
  Boolean(bool),
}

When deriving EnumIs for this enum I get is_u_8, which I want to replace with is_u8 instead. This PR implements the following workaround:

#[derive(EnumIs)]
enum Value {
  #[strum(name = "u8")]
  U8(u8),
  String(String),
  Boolean(bool),
}

This could still be useful for other cases, perhaps one want to rename Boolean to is_bool, for example.

I've also fixed warnings that were emitted while running tests, and some Clippy warnings in the enum_is tests file.

[Mange]

Is there anything else I can do here to help out? :-)

[Peternator7]

Hi @Mange, sorry for the delay here. It's been a busy few weeks. PR looks generally good, and makes sense to me. Two quick things:

1. Could you add the same ability to try_as_*? It seems like a natural extension for symmetry
2. I like the brevity of name, but I think it's going to be a little too confusing that it doesn't change the Display (nor do I think it should). I'm having a difficult time thinking of something brief and descriptive, so maybe something like generated_functions_name or preferred_name_in_fns. Very open to ideas here 😅

[Mange]

Serde had a similar thing with rename. You could use #[serde(rename = "other_name")] and it would affect both serialization and deserialization, oruse #[serde(rename = (deserialize = "original_name", serialize = "new_name"))] to have different names in different derives. [Doc]

Perhaps we could do something similar to this here, either:

#[strum(name = "other_name")] // uses the name for all derives.
#[strum(name = (enum_is = "other_name")] // uses default name for other derives.

// …or, to make configuration appear more scoped, only allow `name` to be for an
// explicit derive kind.
#[strum(enum_is = (name = "other_name"))]