[Vengeance] Fix Vengeance Metamorphosis refresh assertion crash

[taherbert]

Summary

Fixes an assertion crash when Vengeance Metamorphosis is refreshed (e.g. hardcasting Meta during an active Untethered Rage-procced Meta).

Root Cause

Vengeance Metamorphosis (spell 187827) has a Periodic Dummy effect that set_period() picks up during buff_t::init():

Name             : Metamorphosis (id=187827) [Spell Family (107)]
Class            : Vengeance Demon Hunter
Duration         : 15 seconds
Effects          :
#1 (id=273949)   : Apply Aura (6) | Change Model (56)
#2 (id=273950)   : Apply Aura (6) | Increase Health% (133)
#3 (id=283617)   : Apply Aura (6) | Modify Leech% (443)
#4 (id=307168)   : Apply Aura (6) | Add Flat Modifier (107): Spell Effect 4 (32)
#5 (id=314452)   : Apply Aura (6) | Modify Versatility% (471)
#6 (id=329389)   : Apply Aura (6) | Replace Animation (Set) (312)
#7 (id=356685)   : Apply Aura (6) | Periodic Dummy (226): every 2 seconds    <-- this one
#8 (id=775930)   : Apply Aura (6) | Modify Base Resistance (142)
...

Effect 7 is a Periodic Dummy (visual/server logic, not modeled by SimC). During buff_t::init(), set_period() detects this A_PERIODIC_DUMMY subtype and sets refresh_behavior=TICK. However, metamorphosis_buff_t explicitly sets tick_behavior=NONE — so no tick_event is ever created.

When Meta is refreshed, refresh_duration() enters the TICK case and asserts tick_event is non-null → crash.

Chain of events

1. metamorphosis_buff_t constructor sets buff_period = 0, tick_behavior = NONE
2. buff_t::init() → set_period(min()) scans spell data, finds effect 7 (A_PERIODIC_DUMMY, 2s period)
3. Overrides buff_period = 2s and sets refresh_behavior = TICK (since !refresh_behavior_overridden)
4. tick_behavior = NONE prevents tick_event creation in start()
5. UR grants temporary Meta charge → player hardcasts Meta while UR-Meta active → trigger() → refresh() → refresh_duration() → assert(tick_event) at buff.cpp:1637 → crash

Fix

Explicitly call set_refresh_behavior(buff_refresh_behavior::DURATION) in the metamorphosis_buff_t constructor. This sets refresh_behavior_overridden=true, so init() → set_period() respects the override and skips the TICK assignment.

Reproduction

A VDH profile with Untethered Rage that casts metamorphosis on cooldown crashes within ~100 iterations:

# BEFORE (crashes):
Assertion failed: (tick_event), function refresh_duration, file buff.cpp, line 1637.

Test profile (click to expand)

ptr=1
demonhunter="MetaChainTest"
spec=vengeance
level=90
race=night_elf
role=tank
position=front
# Any VDH build with Untethered Rage
talents=CUkAAAAAAAAAAAAAAAAAAAAAAAAYMzMjhZkZmBWMDDmZMzYmZmxYGzsNzYbMzyYMDAAAAzyMYYsswEGmZGLAAAAYgBAAzMADAAAgB
head=,id=153840,ilevel=289
neck=,id=153861,ilevel=289
shoulder=,id=153842,ilevel=289
back=,id=153865,ilevel=289
chest=,id=153837,ilevel=289
wrist=,id=153844,ilevel=289
hands=,id=153839,ilevel=289
waist=,id=153843,ilevel=289
legs=,id=153841,ilevel=289
feet=,id=153838,ilevel=289
finger1=,id=153863,ilevel=289
finger2=,id=153862,ilevel=289
trinket1=,id=153860,ilevel=289
trinket2=,id=153864,ilevel=289
main_hand=,id=248072,ilevel=289
off_hand=,id=248062,ilevel=289

actions.precombat=snapshot_stats
actions=auto_attack
actions+=/metamorphosis
actions+=/immolation_aura
actions+=/spirit_bomb,if=soul_fragments>=4
actions+=/fracture
actions+=/soul_cleave

max_time=120
iterations=100

# AFTER (completes successfully):
Simulating... ( iterations=111, threads=12, ... )