Rust fixes:
- Remove Q0_16 Not arm (was silently returning Bool(false) instead of type error)
- Replace inline floor division with floor_div() calls in MulSatQ16/DivSatQ16
- Fix comment ranges for Q0_16 [-32767, 32767] and Q16_16 [-2147483647, 2147483647]
Go fixes:
- Add euclideanDiv() matching Lean Int.ediv (remainder ≥ 0)
- Use euclideanDiv for MulSatQ16 and DivSatQ16
- Change Locals from []*Val to []Val (dangling pointer fix)
- Step on halted state returns &s, nil (Lean returns Ok s)
- OOB PC returns error instead of silent halt
- Halt does not increment PC (Lean: PC unchanged)
All Go tests pass (9/9)
