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/CMakeLists.txt

@@ -17,4 +17,6 @@ set(OPUS_BUILD_TESTING OFF)
 set(OPUS_BUILD_SHARED_LIBS OFF)
 
 add_subdirectory($ENV{PROJ_PATH}/lib/opus ${CMAKE_CURRENT_BINARY_DIR}/opus)
+target_compile_definitions(opus PRIVATE CUSTOM_SUPPORT)
+target_include_directories(opus PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include)
 target_link_libraries(${COMPONENT_LIB} PUBLIC opus)

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);
+}