v0.8.0

Division footguns — roadmap §3.4 / §3.5.

Added

• E090 — dividing by a statically-zero value (/ 0, / 0.0,
  / BigInt.zero(), / BigDecimal.zero()) is now a compile error. A divide-by-
  zero is a fatal, deterministic sync halt (attempted to divide … by zero).
• W030 — assigning a BigInt / BigInt result to a BigDecimal field is
  flagged: integer division truncates the fraction first (the canonical Uniswap
  "price returns 0" bug). Use .divDecimal(). Integer division into integer
  fields is unaffected (no false positives).
• redstart explain covers both new codes.