fix: add bounds check to prevent out-of-range access in sparse table

[Fruitchan5]

Description of Change

Fix the out-of-bounds access in `getMinimum()` function in `sparse_table_range_queries.cpp`.

Added a boundary check to ensure stable behavior for invalid range queries.

Checklist

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• Added tests and example, test must pass
• Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
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Notes:
This fix prevents crashes due to out-of-bounds access in RMQ function.