optimizer: Implement strength reduction for multiplication, division, and modulo by powers of 2

[MohamedGonem]

Implement strength reduction optimizations in internal/optimizer/simplify_arith.go:

• Replace x * 2^k with x << k (for pure expressions).
• Replace x / 2^k with x >> k (for pure, unsigned integer expressions).
• Replace x % 2^k with x & (2^k - 1) (for pure, unsigned integer expressions).

Files: internal/optimizer/simplify_arith.go (lines 43, 52, 65)