logging: eliminate "fee_estimates" log spam

only log fee estimates if they changed, instead of ~10 times per minute

electrum/network.py

@@ -36,6 +36,7 @@ from typing import NamedTuple, Optional, Sequence, List, Dict, Tuple, TYPE_CHECK
 import traceback
 import concurrent
 from concurrent import futures
+import copy
 
 import aiorpcx
 from aiorpcx import TaskGroup
@@ -531,6 +532,8 @@ class Network(Logger, NetworkRetryManager[ServerAddr]):
         e = self.get_fee_estimates()
         for nblock_target, fee in e.items():
             self.config.update_fee_estimates(nblock_target, fee)
+        if not hasattr(self, "_prev_fee_est") or self._prev_fee_est != e:
+            self._prev_fee_est = copy.copy(e)
             self.logger.info(f'fee_estimates {e}')
         self.notify('fee')