lnpeer: listen to 'fee' events, and run maybe_update_fee()

follow-up 6fb9207a44

> technically the fee estimate of a given bitcoind only changes on new blocks, but because of how we are asking for fee estimates and how we are taking the median of many interfaces, it can change at any time for us

note: running this in the peer taskgroup, for proper exception-handling and logging

electrum/lnpeer.py

@@ -24,6 +24,7 @@ from . import bitcoin, util
 from . import constants
 from .util import (bfh, log_exceptions, ignore_exceptions, chunks, OldTaskGroup,
                    UnrelatedTransactionException, error_text_bytes_to_safe_str, AsyncHangDetector)
+from .util import event_listener, EventListener
 from . import transaction
 from .bitcoin import make_op_return, DummyAddress
 from .transaction import PartialTxOutput, match_script_against_template, Sighash
@@ -64,7 +65,7 @@ if TYPE_CHECKING:
 LN_P2P_NETWORK_TIMEOUT = 20
 
 
-class Peer(Logger):
+class Peer(Logger, EventListener):
     # note: in general this class is NOT thread-safe. Most methods are assumed to be running on asyncio thread.
 
     LOGGING_SHORTCUT = 'P'
@@ -122,6 +123,7 @@ class Peer(Logger):
         self._received_revack_event = asyncio.Event()
         self.received_commitsig_event = asyncio.Event()
         self.downstream_htlc_resolved_event = asyncio.Event()
+        self.register_callbacks()
 
     def send_message(self, message_name: str, **kwargs):
         assert util.get_running_loop() == util.get_asyncio_loop(), f"this must be run on the asyncio thread!"
@@ -633,6 +635,7 @@ class Peer(Logger):
         # note: This method might get called multiple times!
         #       E.g. if you call close_and_cleanup() to cause a disconnection from the peer,
         #       it will get called a second time in handle_disconnect().
+        self.unregister_callbacks()
         try:
             if self.transport:
                 self.transport.close()
@@ -2251,6 +2254,13 @@ class Peer(Logger):
         self._received_revack_event.set()
         self._received_revack_event.clear()
 
+    @event_listener
+    async def on_event_fee(self, *args):
+        async def async_wrapper():
+            for chan in self.channels.values():
+                self.maybe_update_fee(chan)
+        await self.taskgroup.spawn(async_wrapper)
+
     def on_update_fee(self, chan: Channel, payload):
         if chan.peer_state != PeerState.GOOD:  # should never happen
             raise Exception(f"received update_fee in unexpected {chan.peer_state=!r}")