Index request by ID instead of receiving address.

Replace get_key_for_outgoing_invoice, get_key_for_incoming_request
with Invoice.get_id()

When a new request is created, reuse addresses of expired requests (fixes #7927)

The API is changed for the following commands:
 get_request, get_invoice,
 list_requests, list_invoices,
 delete_request, delete_invoice

electrum/invoices.py

@@ -137,6 +137,10 @@ class Invoice(StoredObject):
         # 0 means never
         return self.exp + self.time if self.exp else 0
 
+    def has_expired(self) -> bool:
+        exp = self.get_expiration_date()
+        return bool(exp) and exp < time.time()
+
     def get_amount_msat(self) -> Union[int, str, None]:
         return self.amount_msat