[ty] Treat lambda functions as instances of types.FunctionType (#18431)

Author: lipefree

crates/ty_python_semantic/resources/mdtest/expression/lambda.md

@@ -115,3 +115,22 @@ a5: Callable[[], None] = lambda x: None
 # error: [invalid-assignment]
 a6: Callable[[int], None] = lambda: None
 ```
+
+## Function-like behavior of lambdas
+
+All `lambda` functions are instances of `types.FunctionType` and should have access to the same set
+of attributes.
+
+```py
+x = lambda y: y
+
+reveal_type(x.__code__)  # revealed: CodeType
+reveal_type(x.__name__)  # revealed: str
+reveal_type(x.__defaults__)  # revealed: tuple[Any, ...] | None
+reveal_type(x.__annotations__)  # revealed: dict[str, @Todo(Support for `typing.TypeAlias`)]
+reveal_type(x.__dict__)  # revealed: dict[str, Any]
+reveal_type(x.__doc__)  # revealed: str | None
+reveal_type(x.__kwdefaults__)  # revealed: dict[str, Any] | None
+reveal_type(x.__module__)  # revealed: str
+reveal_type(x.__qualname__)  # revealed: str
+```

crates/ty_python_semantic/src/types/infer.rs

@@ -4956,7 +4956,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         // TODO: Useful inference of a lambda's return type will require a different approach,
         // which does the inference of the body expression based on arguments at each call site,
         // rather than eagerly computing a return type without knowing the argument types.
-        CallableType::single(self.db(), Signature::new(parameters, Some(Type::unknown())))
+        CallableType::function_like(self.db(), Signature::new(parameters, Some(Type::unknown())))
     }
 
     /// Returns the type of the first parameter if the given scope is function-like (i.e. function or lambda).