[codex] Fix QGIS plugin reload cleanup

[giswqs]

Summary

Fix QGIS Plugin Reloader warnings caused by custom plugin toolbars and menus that can remain attached to the QGIS main window after unload().

Changes

• Remove stale plugin toolbars by object name before creating a new toolbar.
• Detach and schedule stale toolbars for deletion during unload.
• Remove stale plugin menus by title before initialization and during unload.
• Keep cleanup best-effort so reload/unload can continue even if QGIS has already detached a widget.

Validation

• Ran python -m py_compile on the changed plugin entry-point file.
• Ran git diff --check.

[Copilot]

Pull request overview

This PR improves QGIS plugin reload/unload hygiene by proactively cleaning up Leafmap’s custom toolbar and menu so they don’t remain attached to the QGIS main window after unload() (reducing QGIS Plugin Reloader warnings).

Changes:

• Add helper methods to locate and detach stale Leafmap toolbars (by objectName) and menus (by title).
• Run cleanup during initGui() before creating a new menu/toolbar to avoid duplicates after reload.
• Run cleanup during unload() to ensure widgets are detached and scheduled for deletion.

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