refactor: enhance type hinting and casting for improved type safety across multiple files

app/services/contact_service.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 from collections.abc import Sequence
 from dataclasses import dataclass
+from typing import cast
 
 from sqlalchemy import select
 
@@ -151,11 +152,11 @@ class ContactService:
     def _build_update_mapping(self, updates: ContactUpdateData) -> dict[str, str | None]:
         payload: dict[str, str | None] = {}
         if updates.name is not UNSET:
-            payload["name"] = updates.name
+            payload["name"] = cast(str | None, updates.name)
         if updates.email is not UNSET:
-            payload["email"] = updates.email
+            payload["email"] = cast(str | None, updates.email)
         if updates.phone is not UNSET:
-            payload["phone"] = updates.phone
+            payload["phone"] = cast(str | None, updates.phone)
         return payload
 
     async def _ensure_no_related_deals(self, contact_id: int) -> None: