Add BaseSettings variant

Summary: #1639

Reviewed By: rchen152

Differential Revision: D87591541

fbshipit-source-id: d4aa47d56652e9f5abfefa60064e26c727b4da65

Author: migeed-z

pyrefly/lib/alt/types/pydantic.rs

@@ -41,4 +41,5 @@ pub enum PydanticModelKind {
     #[default]
     BaseModel,
     RootModel,
+    BaseSettings,
 }