Use smallvec for call path representation (#1960)

This provides a ~10% speed-up for large codebases with `--select ALL`:

![Screen Shot 2023-01-18 at 11 28 20 AM](https://user-images.githubusercontent.com/1309177/213236389-cff50840-6e55-47a3-9164-2e40cbc885f6.png)

src/python/typing.rs

@@ -249,3 +249,13 @@ pub fn is_pep585_builtin(checker: &Checker, expr: &Expr) -> bool {
         PEP_585_BUILTINS_ELIGIBLE.contains(&call_path.as_slice())
     })
 }
+
+pub enum Callable {
+    ForwardRef,
+    Cast,
+    NewType,
+    TypeVar,
+    NamedTuple,
+    TypedDict,
+    MypyExtension,
+}