[ty] Use first matching constructor overload when inferring specializations (#18204)

This is a follow-on to #18155. For the example raised in
https://github.com/astral-sh/ty/issues/370:

```py
import tempfile

with tempfile.TemporaryDirectory() as tmp: ...
```

the new logic would notice that both overloads of `TemporaryDirectory`
match, and combine their specializations, resulting in an inferred type
of `str | bytes`.

This PR updates the logic to match our other handling of other calls,
where we only keep the _first_ matching overload. The result for this
example then becomes `str`, matching the runtime behavior. (We still do
not implement the full [overload resolution
algorithm](https://typing.python.org/en/latest/spec/overload.html#overload-call-evaluation)
from the spec.)

crates/ty_python_semantic/resources/mdtest/generics/legacy/classes.md

@@ -354,6 +354,8 @@ class C(Generic[T]):
     @overload
     def __init__(self: "C[bytes]", x: bytes) -> None: ...
     @overload
+    def __init__(self: "C[int]", x: bytes) -> None: ...
+    @overload
     def __init__(self, x: int) -> None: ...
     def __init__(self, x: str | bytes | int) -> None: ...
 
@@ -369,6 +371,10 @@ C[bytes]("string")  # error: [no-matching-overload]
 C[bytes](b"bytes")
 C[bytes](12)
 
+C[int]("string")  # error: [no-matching-overload]
+C[int](b"bytes")
+C[int](12)
+
 C[None]("string")  # error: [no-matching-overload]
 C[None](b"bytes")  # error: [no-matching-overload]
 C[None](12)

crates/ty_python_semantic/resources/mdtest/generics/pep695/classes.md

@@ -290,6 +290,8 @@ class C[T]:
     @overload
     def __init__(self: C[bytes], x: bytes) -> None: ...
     @overload
+    def __init__(self: C[int], x: bytes) -> None: ...
+    @overload
     def __init__(self, x: int) -> None: ...
     def __init__(self, x: str | bytes | int) -> None: ...
 
@@ -305,6 +307,10 @@ C[bytes]("string")  # error: [no-matching-overload]
 C[bytes](b"bytes")
 C[bytes](12)
 
+C[int]("string")  # error: [no-matching-overload]
+C[int](b"bytes")
+C[int](12)
+
 C[None]("string")  # error: [no-matching-overload]
 C[None](b"bytes")  # error: [no-matching-overload]
 C[None](12)

crates/ty_python_semantic/src/types.rs

@@ -4649,24 +4649,14 @@ impl<'db> Type<'db> {
                     }
                 }
 
-                fn combine_binding_specialization<'db>(
-                    db: &'db dyn Db,
-                    binding: &CallableBinding<'db>,
-                ) -> Option<Specialization<'db>> {
-                    binding
-                        .matching_overloads()
-                        .map(|(_, binding)| binding.inherited_specialization())
-                        .reduce(|acc, specialization| {
-                            combine_specializations(db, acc, specialization)
-                        })
-                        .flatten()
-                }
-
                 let new_specialization = new_call_outcome
                     .and_then(Result::ok)
                     .as_ref()
                     .and_then(Bindings::single_element)
-                    .and_then(|binding| combine_binding_specialization(db, binding))
+                    .into_iter()
+                    .flat_map(CallableBinding::matching_overloads)
+                    .next()
+                    .and_then(|(_, binding)| binding.inherited_specialization())
                     .filter(|specialization| {
                         Some(specialization.generic_context(db)) == generic_context
                     });
@@ -4674,7 +4664,10 @@ impl<'db> Type<'db> {
                     .and_then(Result::ok)
                     .as_ref()
                     .and_then(Bindings::single_element)
-                    .and_then(|binding| combine_binding_specialization(db, binding))
+                    .into_iter()
+                    .flat_map(CallableBinding::matching_overloads)
+                    .next()
+                    .and_then(|(_, binding)| binding.inherited_specialization())
                     .filter(|specialization| {
                         Some(specialization.generic_context(db)) == generic_context
                     });