Fixes for buffers in loops with step size > 1

This MR introduces some additions and fixes for generating CPU loops with step sizes > 1:

• The CPU create_kernel function now exposes a flag to disable the double field write check
• Rewrote get_base_buffer_index to use pure integer arithmetic, and corrected the computation of the buffer base index to correctly incorporate loop step sizes. Added test case to check correctness.
• Added rudimentary evalf functionality to integer division sympy function int_div (its absence lead to an infinite recursion during code generation).
• Added correct printing of integer-typed expressions in CustomSympyPrinter._typed_number.