Fix Signed/Unsigned Integer Comparison Warnings in optimized_WALKSAT.cpp

[danielespo]

This pull request addresses multiple warnings related to the comparison of signed and unsigned integers in optimized_WALKSAT.cpp. These warnings were generated during compilation as a result of using int for loop counters, which were then compared against std::vector::size_type returned by the size() method of standard library containers. Such comparisons can potentially lead to unexpected behaviors and bugs, especially in edge cases.

To resolve these warnings, the loop variables have been changed from int to size_t, which is the appropriate type for indexing and comparing with container sizes. This change ensures type consistency and prevents potential issues arising from comparing signed and unsigned types. The modified code has been thoroughly tested, and the adjustments have been verified to eliminate all relevant compiler warnings without impacting the functionality of the program.

These changes contribute to the overall robustness and maintainability of the codebase by adhering to best practices for type safety in C++.