[red-knot] fix: improve type inference for binary ops on tuples (#16725)

## 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.)

crates/red_knot_python_semantic/resources/mdtest/binary/tuples.md

@@ -0,0 +1,22 @@
+# Binary operations on tuples
+
+## Concatenation for heterogeneous tuples
+
+```py
+reveal_type((1, 2) + (3, 4))  # revealed: tuple[Literal[1], Literal[2], Literal[3], Literal[4]]
+reveal_type(() + (1, 2))  # revealed: tuple[Literal[1], Literal[2]]
+reveal_type((1, 2) + ())  # revealed: tuple[Literal[1], Literal[2]]
+reveal_type(() + ())  # revealed: tuple[()]
+
+def _(x: tuple[int, str], y: tuple[None, tuple[int]]):
+    reveal_type(x + y)  # revealed: tuple[int, str, None, tuple[int]]
+    reveal_type(y + x)  # revealed: tuple[None, tuple[int], int, str]
+```
+
+## Concatenation for homogeneous tuples
+
+```py
+def _(x: tuple[int, ...], y: tuple[str, ...]):
+    reveal_type(x + y)  # revealed: @Todo(full tuple[...] support)
+    reveal_type(x + (1, 2))  # revealed: @Todo(full tuple[...] support)
+```