Adds the Stygian Abyss-era Spell Focusing Sash with full lifecycle,
equipment stat block, and damage sequence behavior:
- New SpellFocusingSash (BaseMiddleTorso) with Brittle, Mana Increase,
Defense Chance Increase, +10 Strength Requirement, and 255/255 durability.
- Context-menu enable/disable on the worn sash.
- Sequence damage modifier: -30 -> 0 over six casts, then +2 per cast
capped at +30 (PvM) or +20 held for five casts (PvP), resetting at the
peak, on target change, on unequip, on disable, on death, and on logout.
- Centralized eligibility gate (SpellFocusingEligible) and shared
SpellHelper.Damage hooks, plus a direct hook in PainSpike.
- Brittle is forced on under Core.SA via AOS.IsBrittle.
- Regression tests covering stats/property ordering, enable state
serialization, context-menu toggle, PvM and PvP sequences, target
resets, disabled state, and non-eligible spells.
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