Coins tab: Speedup for wallets with very many utxos

The essense of this commit is to move the call to
self._update_utxo_count_display() to *before* we rebuild the QTreeWidget
for the Coins tab. The reason this is faster is that updating this header
item count is faster if done with an empty QTreeWidget than if done with
a populated one.

There are no negative effects from this change other than the speedup.

Also in this commit:

- Fix copyright and year for utxo_list.py
- Fix imports for utxo_list.py
- Added some debug-mode only @profiler printing for UTXOList.on_update
  method.

Author: cculianu

electroncash_gui/qt/utxo_list.py

@@ -3,6 +3,9 @@
 # Electrum - lightweight Bitcoin client
 # Copyright (C) 2015 Thomas Voegtlin
 #
+# Electron Cash - lightweight Bitcoin Cash client
+# Copyright (C) 2017-2026 The Electron Cash Developers
+#
 # Permission is hereby granted, free of charge, to any person
 # obtaining a copy of this software and associated documentation files
 # (the "Software"), to deal in the Software without restriction,
@@ -23,17 +26,17 @@
 # CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 from .util import *
-from electroncash.i18n import _, ngettext
-from electroncash.plugins import run_hook
 from electroncash.address import Address
 from electroncash.bitcoin import COINBASE_MATURITY
-from electroncash import cashacct
+from electroncash.i18n import _, ngettext
+from electroncash.plugins import run_hook
+from electroncash.util import profiler, PrintError
 from collections import defaultdict
 from functools import wraps
 from enum import IntEnum
 
 
-class UTXOList(MyTreeWidget):
+class UTXOList(MyTreeWidget, PrintError):
     class Col(IntEnum):
         '''Column numbers. This is to make code in on_update easier to read.
         If you modify these, make sure to modify the column header names in
@@ -79,6 +82,9 @@ def __init__(self, parent=None):
 
         self.cleaned_up = False
 
+    def diagnostic_name(self):
+        return f"{super().diagnostic_name()}/{self.wallet.diagnostic_name()}"
+
     def clean_up(self):
         self.cleaned_up = True
         try: self.parent.ca_address_default_changed_signal.disconnect(self._ca_on_address_default_change)
@@ -110,6 +116,7 @@ def update(self):
         super().update()
 
     @if_not_dead
+    @profiler
     def on_update(self):
         local_maturity_height = (self.wallet.get_local_height()+1) - COINBASE_MATURITY
         prev_selection = self.get_selected() # cache previous selection, if any
@@ -128,6 +135,7 @@ def on_update(self):
             del addr_set  # clean-up. We don't want the below code to ever depend on the existence of this cell.
         else:
             self.utxos = self.wallet.get_utxos(exclude_slp=False, exclude_tokens=False)
+        self._update_utxo_count_display(len(self.utxos))
         for x in self.utxos:
             address = x['address']
             address_text = address.to_ui_string()
@@ -207,7 +215,6 @@ def on_update(self):
             if name in prev_selection:
                 # NB: This needs to be here after the item is added to the widget. See #979.
                 utxo_item.setSelected(True) # restore previous selection
-        self._update_utxo_count_display(len(self.utxos))
 
     def _update_utxo_count_display(self, num_utxos: int):
         headerItem = self.headerItem()