q16_fraction.py uses Python's Fraction for the entire compute path:
- No float, no truncation during intermediate operations
- Quantize to Lean-compatible Q16_16 raw int only at to_raw()
- from_float is the sole float boundary (I/O entry point)
Provides Q16 subclass of Fraction with:
- Exact q16_mul/q16_div/q16_add/q16_sub (no rounding)
- to_raw: truncation toward zero (matches FixedPoint.lean:298)
- to_raw_rounded: round-half-up (alternative output)
Designed for value-set mutation sweeps: explore the full rational
space, quantize only at the final output boundary.
