epic: implement Stage 2 — system compatibility

[edloidas]

Tracking issue for all Stage 2 features from the PRD. These extend the core engine to support popular TTRPG system notations beyond D&D 5e.

Features:

• Exploding dice — 1d6!, 1d6!!, 1d6!p
• Reroll mechanics — 2d6r<2, 2d6ro<3
• Success counting — 10d10>=6, 10d10>=6f1
• Comparison operators — >, >=, <, <=
• PF2e Degrees of Success — 1d20+10 vs 25
• Math functions — floor(), ceil(), round(), abs(), max(), min()
• Percentile dice — d% (alias for d100)
• Fate/Fudge dice — dF (-1, 0, +1)

Each feature will be broken into its own issue when implementation begins.

Rationale

Stage 1 covers the core dice engine for D&D 5e. Stage 2 adds the notation variants needed for PF2e, World of Darkness, Fate, and Savage Worlds — making the library broadly useful across popular systems.

_{Drafted with AI assistance}