Use * for multiple dice rolls and @ for value scaling

[koaning]

Fixes #3

Summary

Changes dice multiplication semantics to match tabletop notation:

• d6 * 3 (or 3 * d6) now rolls three six-sided dice and sums the results — equivalent to d6 + d6 + d6
• d6 @ 3 (or 3 @ d6) scales each face value by a scalar — the previous behavior of *

Multiplying two Dice objects with * still computes the product of independent rolls.

Examples

from dicekit import Dice, exp

d6 = Dice.from_sides(6)

# 3d6: sum of three rolls
three_d6 = d6 * 3
exp(three_d6)  # 10.5

# Scale face values (old * behavior)
scaled = d6 @ 3
exp(scaled)  # 10.5 for a fair d6, but distribution differs from 3d6

Testing

• Updated test_dice_reflected_operations to use @ for scalar scaling
• Added test_dice_mul_counts_rolls and test_dice_matmul_scales_values
• All 17 tests pass