Add IGMP, prepend_buffer/parse_buffer, split UDP header, discovery tests, test all

firmware/include/parse_buffer.h

@@ -0,0 +1,32 @@
+#pragma once
+#include <cstddef>
+#include <cstdint>
+#include <span>
+
+class parse_buffer {
+    const uint8_t* m_data;
+    size_t m_remaining;
+
+public:
+    parse_buffer(std::span<const uint8_t> data)
+        : m_data(data.data()), m_remaining(data.size()) {}
+
+    template <typename T>
+    const T* consume() {
+        if (m_remaining < sizeof(T)) return nullptr;
+        auto* p = reinterpret_cast<const T*>(m_data);
+        m_data += sizeof(T);
+        m_remaining -= sizeof(T);
+        return p;
+    }
+
+    bool skip(size_t len) {
+        if (m_remaining < len) return false;
+        m_data += len;
+        m_remaining -= len;
+        return true;
+    }
+
+    std::span<const uint8_t> remaining() const { return {m_data, m_remaining}; }
+    size_t remaining_size() const { return m_remaining; }
+};