feat: color cast bars green/red by spell interruptibility from Spell.dbc

Load AttributesEx from Spell.dbc for all expansions (Classic/TBC/WotLK/
Turtle). Check SPELL_ATTR_EX_NOT_INTERRUPTIBLE (bit 4 = 0x10) to classify
each cast as interruptible or not when SMSG_SPELL_START arrives.

Target frame and nameplate cast bars now use:
- Green: spell can be interrupted by Kick/Counterspell/Pummel etc.
- Red: spell is immune to interrupt (boss abilities, instant-cast effects)
Both colors pulse faster at >80% completion to signal the closing window.

Adds GameHandler::isSpellInterruptible() and UnitCastState::interruptible.

Data/expansions/classic/dbc_layouts.json

@@ -1,6 +1,6 @@
 {
   "Spell": {
-    "ID": 0, "Attributes": 5, "IconID": 117,
+    "ID": 0, "Attributes": 5, "AttributesEx": 6, "IconID": 117,
     "Name": 120, "Tooltip": 147, "Rank": 129, "SchoolEnum": 1,
     "CastingTimeIndex": 15, "PowerType": 28, "ManaCost": 29, "RangeIndex": 33,
     "DispelType": 4