Fix UC_USELESS_CONDITION SpotBugs warnings and compilation error

Fixed UC_USELESS_CONDITION warnings across 13 files and resolved a compilation error in ComponentGroup.java.
Updated .github/scripts/generate-quality-report.py to fail on this violation.

Notable fixes:
- ComponentGroup.java: Added missing import for Layout class.
- CSSParser.java: Fixed char to byte cast comparison that caused premature EOF on extended ASCII.
- ResourceThreadQueue.java: Fixed variable shadowing and added volatile to cancelled flag.
- UnitValue.java: Fixed condition checking operation type.
- XMLParser.java: Used Character.toLowerCase instead of manual range check.
- Various cleanups in Grid.java, MenuBar.java, Component.java, etc.

Author: google-labs-jules[bot]

CodenameOne/src/com/codename1/ui/ComponentGroup.java

@@ -24,6 +24,7 @@
 package com.codename1.ui;
 
 import com.codename1.ui.layouts.BoxLayout;
+import com.codename1.ui.layouts.Layout;
 
 /**
  * <p>A component group is a container that applies the given UIID to a set of components within it