invoice listeners support on lnd and other fixes around wallets/

lnbits/wallets/base.py

@@ -1,5 +1,5 @@
 from abc import ABC, abstractmethod
-from typing import NamedTuple, Optional
+from typing import NamedTuple, Optional, AsyncGenerator
 
 
 class InvoiceResponse(NamedTuple):
@@ -43,6 +43,15 @@ class Wallet(ABC):
     def get_payment_status(self, checking_id: str) -> PaymentStatus:
         pass
 
+    @abstractmethod
+    def paid_invoices_stream(self) -> AsyncGenerator[str, None]:
+        """
+        this is an async function, but here it is noted without the 'async'
+        prefix because mypy has a bug identifying the signature of abstract
+        methods.
+        """
+        pass
+
 
 class Unsupported(Exception):
     pass