fix: change unsigned long to size_t in compute_barycentric_evaluation header

The implementation (.cpp) already uses size_t but the header declared
unsigned long. On Linux these are the same type, but on Windows LLP64
unsigned long is 32-bit while size_t is 64-bit, causing -Wshorten-64-to-32
when passing domain.size (size_t) to the parameter.

Author: AztecBot

barretenberg/cpp/src/barretenberg/polynomials/polynomial_arithmetic.hpp

@@ -87,7 +87,7 @@ void coset_ifft(std::vector<Fr*> coeffs, const EvaluationDomain<Fr>& domain);
 // src_domain, const EvaluationDomain<Fr>& target_domain);
 
 fr compute_barycentric_evaluation(const fr* coeffs,
-                                  unsigned long num_coeffs,
+                                  size_t num_coeffs,
                                   const fr& z,
                                   const EvaluationDomain<fr>& domain);