Warn on redundant union entries

I think it would help with understand-ability and discover-ability of certain parts of the python type system.
things such as:
- duck typing
- `bool` extends `int`
- `NoneType` extends `object`

```py
i: int | bool = 1
f: float | int = 1
b: bytes | bytearray | memoryview = b''
o: object | None = "AMONGUS"
```
I would expect all these to trigger warnings that the types are redundant.

No source file, test, or entry point is identified in the issue. Start by finding where basedmypy analyzes union members and emits type diagnostics, then trace how subtype relationships are represented. Done means redundant entries such as int | bool and object | None produce warnings, with coverage for the examples in the issue.

Written by the indexing model from the issue text.