Refactors type hints for clarity

Updates type hints in `crud.py`, `helpers.py`, and `models.py` for improved readability and maintainability.

Replaces `Merchant | None` with `Optional[Merchant]` and `list[X]` with `List[X]` for consistency with standard Python typing practices.

services.py

@@ -1,7 +1,8 @@
 import asyncio
 import json
+from typing import List, Optional, Tuple
 
-from bolt11 import decode
+from lnbits.bolt11 import decode
 from lnbits.core.crud import get_wallet
 from lnbits.core.services import create_invoice, websocket_updater
 from loguru import logger
@@ -59,7 +60,7 @@ from .nostr.event import NostrEvent
 
 async def create_new_order(
     merchant_public_key: str, data: PartialOrder
-) -> PaymentRequest | None:
+) -> Optional[PaymentRequest]:
     merchant = await get_merchant_by_pubkey(merchant_public_key)
     assert merchant, "Cannot find merchant for order!"
 
@@ -144,7 +145,7 @@ async def update_merchant_to_nostr(
     merchant: Merchant, delete_merchant=False
 ) -> Merchant:
     stalls = await get_stalls(merchant.id)
-    event: NostrEvent | None = None
+    event: Optional[NostrEvent] = None
     for stall in stalls:
         assert stall.id
         products = await get_products(merchant.id, stall.id)
@@ -229,7 +230,7 @@ async def notify_client_of_order_status(
 
 async def update_products_for_order(
     merchant: Merchant, order: Order
-) -> tuple[bool, str]:
+) -> Tuple[bool, str]:
     product_ids = [i.product_id for i in order.items]
     success, products, message = await compute_products_new_quantity(
         merchant.id, product_ids, order.items
@@ -297,9 +298,9 @@ async def send_dm(
 
 
 async def compute_products_new_quantity(
-    merchant_id: str, product_ids: list[str], items: list[OrderItem]
-) -> tuple[bool, list[Product], str]:
-    products: list[Product] = await get_products_by_ids(merchant_id, product_ids)
+    merchant_id: str, product_ids: List[str], items: List[OrderItem]
+) -> Tuple[bool, List[Product], str]:
+    products: List[Product] = await get_products_by_ids(merchant_id, product_ids)
 
     for p in products:
         required_quantity = next(
@@ -332,6 +333,7 @@ async def process_nostr_message(msg: str):
                 return
             _, event = rest
             event = NostrEvent(**event)
+            
             if event.kind == 0:
                 await _handle_customer_profile_update(event)
             elif event.kind == 4:
@@ -502,7 +504,7 @@ async def _handle_outgoing_dms(
 
 async def _handle_incoming_structured_dm(
     merchant: Merchant, dm: DirectMessage, json_data: dict
-) -> tuple[DirectMessageType, str | None]:
+) -> Tuple[DirectMessageType, Optional[str]]:
     try:
         if dm.type == DirectMessageType.CUSTOMER_ORDER.value and merchant.config.active:
             json_resp = await _handle_new_order(