Add test for box_pool with CamelCase types

[newAM]

Part of #411

[reitermarkus]

What if I want to do

box_pool! {
  MY_POOL: MyPoolData
}

instead? Then I need #[allow(non_camel_case_types)] on the type.

Can we add a second macro case which allows specifying separate idents for type and constant name, something like the following?

box_pool! {
  MY_POOL: MyPool<MyPoolData>
}

[reitermarkus]

Nevermind, I just realized only the type is exposed. I thought the macro generates both a type and constant with the same name.

So this looks like fine as is.

[newAM]

That is a good point though, we should also suppress the clippy lint for SNAKE_CASE and let the user do what they want.