Add MekSearchFilter import to MekHQUnitSelectorDialog

Integrated the MekSearchFilter import to support advanced unit searching capabilities. This update is part of an enhancement for improved search functionality within the MekHQ unit selection dialog.

MekHQ/src/mekhq/gui/dialog/MekHQUnitSelectorDialog.java

@@ -19,6 +19,7 @@
 package mekhq.gui.dialog;
 
 import megamek.client.ui.Messages;
+import megamek.client.ui.advancedsearch.MekSearchFilter;
 import megamek.client.ui.swing.UnitLoadingDialog;
 import megamek.client.ui.swing.dialog.AbstractUnitSelectorDialog;
 import megamek.common.*;