[ty] Add subtyping between Callable types and class literals with __init__ (#17638)

## Summary

Allow classes with `__init__` to be subtypes of `Callable`

Fixes https://github.com/astral-sh/ty/issues/358

## Test Plan

Update is_subtype_of.md

---------

Co-authored-by: Carl Meyer <carl@astral.sh>

crates/ty_python_semantic/resources/mdtest/type_properties/is_assignable_to.md

@@ -608,11 +608,49 @@ c: Callable[[Any], str] = A().g
 ```py
 from typing import Any, Callable
 
+c: Callable[[object], type] = type
 c: Callable[[str], Any] = str
 c: Callable[[str], Any] = int
 
 # error: [invalid-assignment]
 c: Callable[[str], Any] = object
+
+class A:
+    def __init__(self, x: int) -> None: ...
+
+a: Callable[[int], A] = A
+
+class C:
+    def __new__(cls, *args, **kwargs) -> "C":
+        return super().__new__(cls)
+
+    def __init__(self, x: int) -> None: ...
+
+c: Callable[[int], C] = C
+```
+
+### Generic class literal types
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+from typing import Callable
+
+class B[T]:
+    def __init__(self, x: T) -> None: ...
+
+b: Callable[[int], B[int]] = B[int]
+
+class C[T]:
+    def __new__(cls, *args, **kwargs) -> "C[T]":
+        return super().__new__(cls)
+
+    def __init__(self, x: T) -> None: ...
+
+c: Callable[[int], C[int]] = C[int]
 ```
 
 ### Overloads

crates/ty_python_semantic/resources/mdtest/type_properties/is_subtype_of.md

@@ -1219,7 +1219,7 @@ static_assert(is_subtype_of(TypeOf[C], Callable[[], str]))
 #### Classes with `__new__`
 
 ```py
-from typing import Callable
+from typing import Callable, overload
 from ty_extensions import TypeOf, static_assert, is_subtype_of
 
 class A:
@@ -1244,6 +1244,20 @@ static_assert(is_subtype_of(TypeOf[E], Callable[[], C]))
 static_assert(is_subtype_of(TypeOf[E], Callable[[], B]))
 static_assert(not is_subtype_of(TypeOf[D], Callable[[], C]))
 static_assert(is_subtype_of(TypeOf[D], Callable[[], B]))
+
+class F:
+    @overload
+    def __new__(cls) -> int: ...
+    @overload
+    def __new__(cls, x: int) -> "F": ...
+    def __new__(cls, x: int | None = None) -> "int | F":
+        return 1 if x is None else object.__new__(cls)
+
+    def __init__(self, y: str) -> None: ...
+
+static_assert(is_subtype_of(TypeOf[F], Callable[[int], F]))
+static_assert(is_subtype_of(TypeOf[F], Callable[[], int]))
+static_assert(not is_subtype_of(TypeOf[F], Callable[[str], F]))
 ```
 
 #### Classes with `__call__` and `__new__`
@@ -1266,6 +1280,123 @@ static_assert(is_subtype_of(TypeOf[F], Callable[[], int]))
 static_assert(not is_subtype_of(TypeOf[F], Callable[[], str]))
 ```
 
+#### Classes with `__init__`
+
+```py
+from typing import Callable, overload
+from ty_extensions import TypeOf, static_assert, is_subtype_of
+
+class A:
+    def __init__(self, a: int) -> None: ...
+
+static_assert(is_subtype_of(TypeOf[A], Callable[[int], A]))
+static_assert(not is_subtype_of(TypeOf[A], Callable[[], A]))
+
+class B:
+    @overload
+    def __init__(self, a: int) -> None: ...
+    @overload
+    def __init__(self) -> None: ...
+    def __init__(self, a: int | None = None) -> None: ...
+
+static_assert(is_subtype_of(TypeOf[B], Callable[[int], B]))
+static_assert(is_subtype_of(TypeOf[B], Callable[[], B]))
+
+class C: ...
+
+# TODO: This assertion should be true once we understand `Self`
+# error: [static-assert-error] "Static assertion error: argument evaluates to `False`"
+static_assert(is_subtype_of(TypeOf[C], Callable[[], C]))
+
+class D[T]:
+    def __init__(self, x: T) -> None: ...
+
+static_assert(is_subtype_of(TypeOf[D[int]], Callable[[int], D[int]]))
+static_assert(not is_subtype_of(TypeOf[D[int]], Callable[[str], D[int]]))
+```
+
+#### Classes with `__init__` and `__new__`
+
+```py
+from typing import Callable, overload, Self
+from ty_extensions import TypeOf, static_assert, is_subtype_of
+
+class A:
+    def __new__(cls, a: int) -> Self:
+        return super().__new__(cls)
+
+    def __init__(self, a: int) -> None: ...
+
+static_assert(is_subtype_of(TypeOf[A], Callable[[int], A]))
+static_assert(not is_subtype_of(TypeOf[A], Callable[[], A]))
+
+class B:
+    def __new__(cls, a: int) -> int:
+        return super().__new__(cls)
+
+    def __init__(self, a: str) -> None: ...
+
+static_assert(is_subtype_of(TypeOf[B], Callable[[int], int]))
+static_assert(not is_subtype_of(TypeOf[B], Callable[[str], B]))
+
+class C:
+    def __new__(cls, *args, **kwargs) -> "C":
+        return super().__new__(cls)
+
+    def __init__(self, x: int) -> None: ...
+
+# Not subtype because __new__ signature is not fully static
+static_assert(not is_subtype_of(TypeOf[C], Callable[[int], C]))
+static_assert(not is_subtype_of(TypeOf[C], Callable[[], C]))
+
+class D: ...
+
+class E:
+    @overload
+    def __new__(cls) -> int: ...
+    @overload
+    def __new__(cls, x: int) -> D: ...
+    def __new__(cls, x: int | None = None) -> int | D:
+        return D()
+
+    def __init__(self, y: str) -> None: ...
+
+static_assert(is_subtype_of(TypeOf[E], Callable[[int], D]))
+static_assert(is_subtype_of(TypeOf[E], Callable[[], int]))
+
+class F[T]:
+    def __new__(cls, x: T) -> "F[T]":
+        return super().__new__(cls)
+
+    def __init__(self, x: T) -> None: ...
+
+static_assert(is_subtype_of(TypeOf[F[int]], Callable[[int], F[int]]))
+static_assert(not is_subtype_of(TypeOf[F[int]], Callable[[str], F[int]]))
+```
+
+#### Classes with `__call__`, `__new__` and `__init__`
+
+If `__call__`, `__new__` and `__init__` are all present, `__call__` takes precedence.
+
+```py
+from typing import Callable
+from ty_extensions import TypeOf, static_assert, is_subtype_of
+
+class MetaWithIntReturn(type):
+    def __call__(cls) -> int:
+        return super().__call__()
+
+class F(metaclass=MetaWithIntReturn):
+    def __new__(cls) -> str:
+        return super().__new__(cls)
+
+    def __init__(self, x: int) -> None: ...
+
+static_assert(is_subtype_of(TypeOf[F], Callable[[], int]))
+static_assert(not is_subtype_of(TypeOf[F], Callable[[], str]))
+static_assert(not is_subtype_of(TypeOf[F], Callable[[int], F]))
+```
+
 ### Bound methods
 
 ```py