feat(verification): add infrastructure for user verification

- **FSM States:** Added `VerificationStates` to manage the dialog flow.
- **Services:** Implemented `get_or_create_user` and `verify_student` to encapsulate business logic.
- **Middleware Chain:** Refactored the middleware to a clean, sequential chain (`Database`, `TelegramUser`, `Registration`) where each has a single responsibility.
- **Verification Status:** Introduced a `VerificationStatus` enum for clear and type-safe results from the verification service.

src/bot/services/verification.py

@@ -1,5 +1,4 @@
 __all__ = [
-    "check_registration_status",
     "verify_student"
 ]
 
@@ -13,32 +12,11 @@ from src.database.models import Student, TelegramUser
 from .types.verification_statuses import VerificationStatus
 
 
-async def check_registration_status(
-    tg_id: int,
-    session: AsyncSession,
-) -> bool:
-    """
-    Checks if a tg user is linked to a university member.
-
-    Args:
-        tg_id (int): user's telegram id.
-        session (AsyncSession): database session.
-
-    Returns:
-        bool: True if the user is registered (linked), otherwise False.
-    """
-    query = select(TelegramUser).where(TelegramUser.id == tg_id)
-    result = await session.execute(query)
-    user = result.scalar_one_or_none()
-
-    return user is not None and user.university_member_id is not None
-
-
 async def verify_student(
     tg_user: TelegramUser,
     name: str,
     student_id: int,
-    group_id: int,
+    group_id: str,
     session: AsyncSession,
 ) -> VerificationStatus:
     """