put opus' allocations into internal ram

it's a pretty chonky codec, but this seems like the best way to tame its
performance.

lib/opusfile/include/custom_support.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include "esp_heap_caps.h"
+#include "opus_defines.h"
+
+#define OVERRIDE_OPUS_ALLOC
+#define OVERRIDE_OPUS_FREE
+
+static OPUS_INLINE void *opus_alloc (size_t size)
+{
+   return heap_caps_malloc(size, MALLOC_CAP_8BIT | MALLOC_CAP_INTERNAL);
+}
+
+static OPUS_INLINE void opus_free (void *ptr)
+{
+   heap_caps_free(ptr);
+}