Related to #387

## Synopsis

After #387, the following snippet fails to compile:
```rust
#[derive(Debug)]
struct AssocType<I: Iterator> {
    iter: I,
    elem: Option<I::Item>,
}
```
This happens, because the implied bound `Option<I::Item>: Debug` is not
generated.

## Solution

Correct the `ContainsGenericsExt::contains_generics()` implementations
to consider associated types of the type parameter.

#400)

## Synopsis

For `!` never type used in trait signatures, `rustc` emits
`unreachable_code` warning ignoring the `#[automatically_derived]`
attribute.

## Solution

Add `#[allow(unreachable_code)]` to generated `impl`s to suppress such
warnings for `!` and similar types.

…410)

Resolves #409

## Synopsis

Fixes the "abiguous associated item" error when deriving `TryFrom`,
`TryInto` or `FromStr` when those types have an associated item called
`Error` or `Err` respectively.

All these derives produce that error:
```rust
use derive_more::*;

#[derive(TryFrom)]
#[try_from(repr)]
#[repr(u8)]
enum LogLevel {
    Error,
}

#[derive(FromStr)]
enum EnumNoFields {
    Err,
}

#[derive(TryInto)]
enum MixedInts {
    Foo(LogLevel),
}
```

## Solution

Replace  `Self::Error` with the type that's behind it.

As was decided in #405, the crate's root should re-export only macros.
Re-exporting of macros along with their corresponding traits should be
moved to `with_trait` module.

Co-authored-by: Jelte Fennema-Nio <github-tech@jeltef.nl>

## Synopsis

`cargo test --no-default-features --features=full` fails imposing
problems on other CIs.

## Solution

- Consider testing `full` Cargo feature in `test-features` CI job to
handle such regressions.
- Update the relevant tests to run under `no_std` too.

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

…, #411)

- fix top-level `#[display("...")]` attribute on an enum being incorrectly treated as transparent or wrapping
- make top-level `#[display("...")]` attribute on an enum to have defaulting behavior instead of replacing when no wrapping is possible (no `_variant` placeholder)

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

)