Replace `__product_group` method with `__product_generate` and `__product_next`.
This change eliminates the need for Ruby to perform internal state calculations, allowing it to simply receive the results.

Summary of Changes

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This pull request significantly optimizes the Array#product method by shifting the complex iteration logic and state management from Ruby to C. By introducing a C-level generator, the Ruby implementation of product now simply requests the next product group, eliminating the need for Ruby to perform internal state calculations and improving overall performance.

Highlights

Ruby Array#product Refactoring: The Array#product method in mrblib/array.rb was refactored to delegate its core logic to new C-level helper methods, __product_generate and __product_next.
C-level Generator Implementation: New C functions, ary_product_generate and ary_product_next, were introduced in src/array.c to manage the iteration state and yield product groups more efficiently. This includes a new ary_product_generator struct for state management.
Optimized Group Fetching: The internal ary_product_group C function was renamed to ary_product_fetch and its signature and logic were updated to serve as a helper for fetching individual product groups, now utilized by the new generator functions.
Reduced Ruby Overhead: The change eliminates the need for Ruby to perform internal state calculations for Array#product, allowing it to simply receive the results from the C-level generator, leading to performance optimization.

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Comment on lines +1457 to +1468

		ary_product_next(mrb_state *mrb, mrb_value self)
		{
		mrb_value arys;
		struct ary_product_generator *g;
		mrb_get_args(mrb, "Ad", &arys, &g, &ary_product_generator_type);

		if (g->cursor >= g->total) {
		return mrb_nil_value();
		}

		return ary_product_fetch(mrb, self, arys, g->cursor++);
		}