⚡ Optimize const_roll_table::roll hot path

[perim]

💡 What: Replaced std::vector::at() with the array subscript operator [] for accessing probability and alias elements in const_roll_table::roll (dice.h:117).
🎯 Why: The at() method includes an bounds check on every access, which adds unnecessary overhead in a hot path. Since the index i is deterministically generated to be strictly within the bounds [0, size - 1], the bounds check is redundant. Using [] avoids this overhead, making the method faster.
📊 Measured Improvement:

• Baseline performance for 400,000 rolls of const_roll_table: ~4,182,454 cycles.
• Optimized performance for 400,000 rolls: ~3,863,542 cycles.
• Improvement: Reduced cycle count by ~318,912 cycles (~7.6% improvement in the CRT benchmark).

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PR created automatically by Jules for task 833052734268679771 started by @perim

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