move callback_list, parse_buffer, prepend_buffer, static_vector, timer_queue into util; util links pico_stdlib for timer_queue

util/static_vector.h

@@ -0,0 +1,36 @@
+#pragma once
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+
+// Fixed-capacity contiguous container: std::vector's interface with std::array's
+// storage. Used for response payloads sized at parse time but bounded at compile
+// time, where heap allocation is unavailable or undesirable.
+template <typename T, size_t Capacity>
+class static_vector {
+    T m_data[Capacity];
+    size_t m_size = 0;
+
+public:
+    void push_back(const T &v) {
+        if (m_size < Capacity) m_data[m_size++] = v;
+    }
+
+    void clear() { m_size = 0; }
+
+    size_t size() const { return m_size; }
+    size_t capacity() const { return Capacity; }
+    bool full() const { return m_size >= Capacity; }
+    bool empty() const { return m_size == 0; }
+
+    T *data() { return m_data; }
+    const T *data() const { return m_data; }
+
+    T &operator[](size_t i) { return m_data[i]; }
+    const T &operator[](size_t i) const { return m_data[i]; }
+
+    T *begin() { return m_data; }
+    T *end() { return m_data + m_size; }
+    const T *begin() const { return m_data; }
+    const T *end() const { return m_data + m_size; }
+};