## Summary
This PR includes minor improvements to binary operation inference,
specifically for tuple concatenation.
### Before
```py
reveal_type((1, 2) + (3, 4)) # revealed: @Todo(return type of decorated function)
# If TODO is ignored, the revealed type would be `tuple[1|2|3|4, ...]`
```
The `builtins.tuple` type stub defines `__add__`, but it appears to only
work for homogeneous tuples. However, I think this limitation is not
ideal for many use cases.
### After
```py
reveal_type((1, 2) + (3, 4)) # revealed: tuple[Literal[1], Literal[2], Literal[3], Literal[4]]
```
## Test Plan
### Added
- `mdtest/binary/tuples.md`
### Affected
- `mdtest/slots.md` (a test have been moved out of the `False-Negative`
block.)
