feat(data): SPSC ring buffer, incremental min/max LOD pyramid, series types

tests/test_ring_buffer.cpp

@@ -0,0 +1,19 @@
+#include "harness.hpp"
+#include <plot/data/ring_buffer.hpp>
+
+PLOT_TEST(ring_wraps_and_keeps_latest) {
+  plot::data::RingBuffer<f32> r(8);        // capacity rounded up to a power of two
+  for (int i = 0; i < 20; ++i) r.push(f32(i));
+  PLOT_CHECK(r.size() == 8);
+  PLOT_CHECK_NEAR(r[0], 12.0);             // oldest retained
+  PLOT_CHECK_NEAR(r[7], 19.0);             // newest
+}
+PLOT_TEST(ring_clear_resets) {
+  plot::data::RingBuffer<f32> r(8);
+  for (int i = 0; i < 5; ++i) r.push(f32(i));
+  r.clear();
+  PLOT_CHECK(r.size() == 0);
+  r.push(42.0f);
+  PLOT_CHECK(r.size() == 1);
+  PLOT_CHECK_NEAR(r[0], 42.0);
+}