Equalize dock zone sizes on startup (#265)

* Fix unit visibility change not propagating to other views

`get_visible_unit_ids()` returned a direct reference to the internal
`_visible_unit_ids` list. Callers that snapshot the list before and after
`set_unit_visibility()` to detect changes were comparing the same mutated
object, so the comparison always found no difference and never triggered
`notify_unit_visibility_changed()`.

Return a copy instead so before/after comparisons work correctly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Equalize dock zone sizes on startup

Dock widgets created by splitDockWidget() have uneven default sizes.
Add a showEvent hook that calls resizeDocks() with equal weights after
the window is visible, so all zones start proportionally sized.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Use processEvents instead of timer for dock equalization

Replace QTimer.singleShot(100ms) hack with QApplication.processEvents()
to flush pending layout events synchronously before calling resizeDocks.
Deterministic and avoids arbitrary delay.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Fix dock equalization not working on macOS

Replace synchronous processEvents() + resizeDocks() with a deferred
QTimer.singleShot(0) call. On macOS, the Cocoa window system performs
a layout pass after Qt's showEvent, overwriting sizes set synchronously.
The deferred call ensures resizeDocks runs after the native layout completes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: xiao-1011

spikeinterface_gui/backend_qt.py

@@ -255,6 +255,23 @@ def create_main_layout(self):
             # make visible the first of each zone
             self.docks[view_name0].raise_()
 
+    def showEvent(self, event):
+        super().showEvent(event)
+        if not hasattr(self, '_splitters_equalized'):
+            self._splitters_equalized = True
+            # On macOS, the native Cocoa window system performs a layout pass after
+            # Qt's showEvent, overwriting any sizes set synchronously. A deferred
+            # call via QTimer.singleShot ensures resizeDocks runs after both Qt and
+            # the macOS window server have finished laying out the docks.
+            QT.QTimer.singleShot(0, self._equalize_dock_sizes)
+
+    def _equalize_dock_sizes(self):
+        all_docks = [dock for dock in self.docks.values() if dock.isVisible()]
+        if all_docks:
+            size_weight = 1
+            self.resizeDocks(all_docks, [size_weight] * len(all_docks), QT.Qt.Horizontal)
+            self.resizeDocks(all_docks, [size_weight] * len(all_docks), QT.Qt.Vertical)
+
     def make_half_layout(self, widgets_zone, left_or_right):
         """
         Function contains the logic for the greedy layout. Given the 2x2 box of zones