refactor(codec): de-Qt oakcodec and wrap it in a pure C ABI; switch common handles to refcounted value structs

- oakcodec: de-Qt all 20 sources (QThread decode loop -> std::thread,
  QObject/signals -> callbacks), pure C ABI in include/codec with
  refcounted neutral handles (OakFrame/OakDecoder/OakEncoder),
  framemanager moved in from render, frame_to_buffer/buffer_to_frame
  moved in from oakcommon oiioutils, codec->task via submit callback
  (M8 will register), all cross-module calls go through the other
  side's C API, -fvisibility=hidden + OAKCODEC_API
- oakcommon: handles become refcounted value structs
  {ctx, addref, release, abi_version} (FFmpeg-style), pass-by-value
  signatures, free() as release wrapper; init_from_native/get_native
  for copyable value objects; OakCommonXxx renamed to OakXxx
- oakcommon: add logging (log_debug/info/warning/critical with level
  filtering and sink injection) + printf-style oakcommon_log C wrapper
- oakrender: add CancelAtom C API family; complete
  oakrender_color_processor_convert_frame; fix get_processor() missing
  definition and OCIO env var lookup
- tests: oakcommon 174, oaknode 96, oakrender 42, oakcodec 18, all
  green in their standalone builds

include/node/block.h

@@ -189,7 +189,7 @@ int oaknode_clip_get_maintain_audio_pitch(OakNodeBlock *clip, int *maintain);
 int oaknode_clip_set_maintain_audio_pitch(OakNodeBlock *clip, int maintain);
 
 /**
- * @brief Loop mode, one of the OakCommonLoopMode values
+ * @brief Loop mode, one of the OakLoopMode values
  * (olive::ClipBlock::loop_mode/set_loop_mode).
  */
 int oaknode_clip_get_loop_mode(OakNodeBlock *clip, int *loop_mode);