feat(track-core): add portable training runtimes

Move scheme and PID training runtime behavior into the pure track_core layer and expose render sinks for injected strip application.

Add ESP compatibility adapters, Python bindings/test scaffolding, and in-memory render support so app_track_bt can consume core render and runtime logic without duplicating it.

Cover circular/linear rendering boundaries, all scheme runtime types, scheme render_to parity, PID sample de-duplication, speed suppression, and live tuning in track-core tests.

src/memory_strip.cpp

@@ -3,6 +3,41 @@
 #include <algorithm>
 
 namespace track_core {
+namespace {
+
+MemoryStrip *memory_strip_from_context(void *context) {
+    return static_cast<MemoryStrip *>(context);
+}
+
+TrackError memory_strip_clear(void *context) {
+    auto *strip = memory_strip_from_context(context);
+    if (strip == nullptr) {
+        return TrackError::invalid_arg;
+    }
+    return strip->clear();
+}
+
+TrackError memory_strip_fill(
+    void *context,
+    std::uint16_t start_led,
+    std::uint16_t led_count,
+    Color color) {
+    auto *strip = memory_strip_from_context(context);
+    if (strip == nullptr) {
+        return TrackError::invalid_arg;
+    }
+    return strip->fill(start_led, led_count, color);
+}
+
+TrackError memory_strip_show(void *context) {
+    auto *strip = memory_strip_from_context(context);
+    if (strip == nullptr) {
+        return TrackError::invalid_arg;
+    }
+    return strip->show();
+}
+
+} // namespace
 
 MemoryStrip::MemoryStrip(std::size_t led_count)
     : pixels_(led_count, Color::black()) {}
@@ -60,13 +95,16 @@ std::span<const Color> MemoryStrip::pixels() const {
 }
 
 TrackError apply_render_plan(MemoryStrip &strip, const TrackRenderPlan &plan) {
-    for (std::size_t i = 0; i < plan.span_count; ++i) {
-        const auto &span = plan.spans[i];
-        if (const auto err = strip.fill(span.start_led, span.led_count, span.color); err != TrackError::ok) {
-            return err;
-        }
-    }
-    return TrackError::ok;
+    return apply_render_plan(make_memory_strip_sink(strip), plan);
+}
+
+TrackRenderSink make_memory_strip_sink(MemoryStrip &strip) {
+    return TrackRenderSink{
+        .context = &strip,
+        .clear = memory_strip_clear,
+        .fill = memory_strip_fill,
+        .show = memory_strip_show,
+    };
 }
 
 } // namespace track_core