Change the for loops counter type to size_t

[MertGunduz]

For loops are using this in the current codebase:

for (int i = 0; i < NUM; i++)
{
      // code
}

We want to make it like this for better readability and optimisation:

for (size_t i = 0; i < NUM; i++)
{
      // code
}

[MertGunduz]

Finished 🚀