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/common/dropworkflowbehavior.h

@@ -35,7 +35,7 @@ extern "C" {
  * src/common/src/dropworkflowbehavior.h; enumerator order and values
  * must stay identical because the config layer persists them as ints.
  */
-enum OakCommonDropWorkflowBehavior {
+enum OakDropWorkflowBehavior {
 	OAKCOMMON_DWS_ASK = 0, /**< Ask the user every time. */
 	OAKCOMMON_DWS_AUTO = 1, /**< Automatically create a sequence. */
 	OAKCOMMON_DWS_MANUAL = 2, /**< Never create; import manually. */
@@ -43,7 +43,7 @@ enum OakCommonDropWorkflowBehavior {
 };
 
 /**
- * @brief Check whether value is a valid OakCommonDropWorkflowBehavior.
+ * @brief Check whether value is a valid OakDropWorkflowBehavior.
  *
  * @param value Integer behavior value (e.g. read from config).
  * @return 1 if valid, 0 otherwise (this is a predicate, not a status
@@ -57,7 +57,7 @@ int oakcommon_drop_workflow_behavior_is_valid(int value);
  * Two-segment string getter: if buf is NULL or buf_size is too small,
  * nothing is written. Invalid values yield "UNKNOWN".
  *
- * @param value One of OakCommonDropWorkflowBehavior.
+ * @param value One of OakDropWorkflowBehavior.
  * @param buf Destination buffer, may be NULL to query the size.
  * @param buf_size Size of buf in bytes.
  * @return Required buffer size in bytes including the terminating NUL