add Chapter18

Chapter18/cib/libs/interrupt/fwd.hpp

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+#pragma once
+
+#include <stdx/compiler.hpp>
+
+#include <cstddef>
+#include <cstdint>
+
+namespace interrupt {
+enum struct irq_num_t : std::uint32_t {};
+using priority_t = std::size_t;
+
+inline namespace literals {
+// NOLINTNEXTLINE(google-runtime-int)
+CONSTEVAL auto operator""_irq(unsigned long long int v) -> irq_num_t {
+    return static_cast<irq_num_t>(v);
+}
+} // namespace literals
+} // namespace interrupt