Fixes #8990.

Description of the problem being solved:

Fixed poison stacks showing 0 despite 100% poison chance when using multi-step damage conversion chains (e.g., Cold→Fire→Chaos→Poison). The issue occurred because Path of Building's ailment calculations only considered unconverted damage portions and didn't account for damage that becomes eligible for ailments through conversion chains.

Root causes addressed:

• calcAilmentSourceDamage() only used unconverted damage, ignoring conversion contributions
• Poison chance calculation didn't include ChaosPoisonChance for both hit and crit scenarios
• No automatic enabling of CanPoison flags for damage types that convert to Chaos
• Same issues affected ignite calculations with fire conversions

Steps taken to verify a working solution:

• Test Setup: 2x The Consuming Dark daggers + 2x The Pyre rings + Cold Snap of Power skill
• Conversion Chain: Cold (100%) → Fire (40% via Pyre) → Chaos (12% via Consuming Dark) → Poison (60% chance per dagger)
• Before Fix: Poison DPS = 0, Poison Stacks = 0 (capped to 1)
• After Fix: Poison DPS = 1,178.9, Poison Stacks = 0.67, Poison Chance = 100%
• Regression Testing: Verified pure chaos poison builds still work correctly
• Edge Case Testing: Tested partial conversions and multiple ailment scenarios

Link to a build that showcases this PR:

Path of Building test build:

• Skill: Cold Snap of Power
• Weapons: 2x The Consuming Dark (Fiend Dagger)
• Rings: 2x The Pyre (Sapphire Ring)
• Expected: Poison calculations now work with conversion chains

Before fix:

Poison DPS: 0, Poison Stacks: 0, despite showing 100% poison chance

After fix:

Poison DPS: 1,178.9, Poison Stacks: 0.67, Poison Chance: 100% (working correctly)

Technical Changes:

• Added calcAilmentConversionMultiplier() function for multi-step conversion tracking
• Enhanced calcAilmentSourceDamage() to use conversion chains instead of just unconverted portions
• Added automatic CanPoison/CanIgnite flag enabling for converted damage types
• Fixed poison chance calculations to include ChaosPoisonChance for both hits and crits
• Applied same fixes to ignite calculations for fire conversions
• Added comprehensive safety checks to prevent nil reference errors