[Warlock] Destruction apex talent

[stahlscott]

Initial implementation of Embers of Nihilam apex talent for warlock destruction spec

Needs verification:

• Rank 1 proc rate (Incinerate → Echo of Sargeras) is not in spell data: using 25% placeholder, configurable via rng_settings

Implementation notes:

• Visions of Nihilam (rank 2/3) scaling: spell data auto-scales base_value with talent rank via op=mul, values=(1,2), so .percent() alone gives the correct value (4% at rank 1, 8% at rank 2)
• Rank 4 uses a helper for all affected spells (CB, SB, RoF) to handle the case where there's no target present - even though CB/SB always has a target as of now, figured it was safer for future proofing
• Rank 1 (proc chance, no ICD) and rank 3 (guaranteed, 0.5s ICD) are intentionally independent as they are separate talent effects with different gating mechanics

[nyterage]

Looks good generally, only one comment