register channel listeners instead of callbacks.

makes for a little less black magic and more reasonable use of nurseries
and less unnecessary pseudo-requests.

lnbits/core/tasks.py

@@ -1,15 +1,22 @@
 import trio  # type: ignore
 from typing import List
 
-from .models import Payment
+from lnbits.tasks import register_invoice_listener
 
 sse_listeners: List[trio.MemorySendChannel] = []
 
 
-async def on_invoice_paid(payment: Payment):
-    for send_channel in sse_listeners:
-        try:
-            send_channel.send_nowait(payment)
-        except trio.WouldBlock:
-            print("removing sse listener", send_channel)
-            sse_listeners.remove(send_channel)
+async def register_listeners():
+    invoice_paid_chan_send, invoice_paid_chan_recv = trio.open_memory_channel(5)
+    register_invoice_listener(invoice_paid_chan_send)
+    await wait_for_paid_invoices(invoice_paid_chan_recv)
+
+
+async def wait_for_paid_invoices(invoice_paid_chan: trio.MemoryReceiveChannel):
+    async for payment in invoice_paid_chan:
+        for send_channel in sse_listeners:
+            try:
+                send_channel.send_nowait(payment)
+            except trio.WouldBlock:
+                print("removing sse listener", send_channel)
+                sse_listeners.remove(send_channel)