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/current.h

@@ -22,12 +22,27 @@
 #define OAK_EDITOR_CURRENT_H
 
 #include "common/error.h"
+#include "common/handle.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-typedef struct OakCommonCurrent OakCommonCurrent;
+/**
+ * @brief Neutral by-value handle to the process-wide Current singleton.
+ *
+ * Uses the standard handle layout (see common/handle.h) but with
+ * singleton semantics: ctx points to a statically allocated object that
+ * lives until process exit, so addref() and release() are intentionally
+ * no-ops and never destroy anything. abi_version is always
+ * OAKCOMMON_ABI_VERSION.
+ */
+typedef struct OakCurrent {
+	void *ctx; /**< Opaque pointer to the singleton object. */
+	void (*addref)(void *ctx); /**< No-op (singleton). */
+	void (*release)(void *ctx); /**< No-op (singleton). */
+	uint32_t abi_version; /**< OAKCOMMON_ABI_VERSION. */
+} OakCurrent;
 
 /**
  * @brief Destructor callback for objects handed to Current slots.
@@ -35,23 +50,24 @@ typedef struct OakCommonCurrent OakCommonCurrent;
  * Called when the slot is overwritten or cleared. May be NULL if the
  * caller keeps ownership of the object.
  */
-typedef void (*OakCommonDestroyFn)(void *obj);
+typedef void (*OakDestroyFn)(void *obj);
 
 /**
  * @brief Return a handle to the process-wide Current singleton.
  *
- * The returned handle is borrowed: it is valid for the lifetime of the
- * process and must not be freed with oakcommon_current_free() more
- * than out of symmetry (free is a no-op for the singleton).
+ * The returned handle is borrowed: its ctx is valid for the lifetime of
+ * the process. addref/release on it are no-ops; calling
+ * oakcommon_current_free() is allowed for symmetry and does nothing.
  */
-OakCommonCurrent *oakcommon_current_instance(void);
+OakCurrent oakcommon_current_instance(void);
 
 /**
  * @brief Release a Current handle.
  *
- * No-op: the underlying object is a singleton. Safe to call with NULL.
+ * No-op: the underlying object is a singleton whose release() never
+ * destroys anything. Safe to call with NULL or a ctx == NULL handle.
  */
-void oakcommon_current_free(OakCommonCurrent *self);
+void oakcommon_current_free(OakCurrent *self);
 
 /**
  * @brief Store a pointer in a Current slot, taking over destruction.
@@ -63,16 +79,16 @@ void oakcommon_current_free(OakCommonCurrent *self);
  * @param obj Opaque pointer to the external object (e.g. a
  * VideoParams), or NULL to clear.
  * @param destroy Optional destructor invoked when the slot is replaced.
- * @return OAKCOMMON_OK on success, OAKCOMMON_E_INVALID if self is NULL.
+ * @return OAKCOMMON_OK on success, OAKCOMMON_E_INVALID if self.ctx is NULL.
  */
-int oakcommon_current_set_video_params(OakCommonCurrent *self, void *obj,
-				       OakCommonDestroyFn destroy);
-int oakcommon_current_set_audio_params(OakCommonCurrent *self, void *obj,
-				       OakCommonDestroyFn destroy);
-int oakcommon_current_set_plugin_host(OakCommonCurrent *self, void *obj,
-				      OakCommonDestroyFn destroy);
-int oakcommon_current_set_plugin_cache(OakCommonCurrent *self, void *obj,
-				       OakCommonDestroyFn destroy);
+int oakcommon_current_set_video_params(OakCurrent self, void *obj,
+				       OakDestroyFn destroy);
+int oakcommon_current_set_audio_params(OakCurrent self, void *obj,
+				       OakDestroyFn destroy);
+int oakcommon_current_set_plugin_host(OakCurrent self, void *obj,
+				      OakDestroyFn destroy);
+int oakcommon_current_set_plugin_cache(OakCurrent self, void *obj,
+				       OakDestroyFn destroy);
 
 /**
  * @brief Fetch the raw pointer currently stored in a slot.
@@ -82,23 +98,23 @@ int oakcommon_current_set_plugin_cache(OakCommonCurrent *self, void *obj,
  *
  * @param self Handle from oakcommon_current_instance().
  * @param out Receives the stored pointer.
- * @return OAKCOMMON_OK on success, OAKCOMMON_E_INVALID if self or out
- * is NULL.
+ * @return OAKCOMMON_OK on success, OAKCOMMON_E_INVALID if self.ctx or
+ * out is NULL.
  */
-int oakcommon_current_get_video_params(OakCommonCurrent *self, void **out);
-int oakcommon_current_get_audio_params(OakCommonCurrent *self, void **out);
-int oakcommon_current_get_plugin_host(OakCommonCurrent *self, void **out);
-int oakcommon_current_get_plugin_cache(OakCommonCurrent *self, void **out);
+int oakcommon_current_get_video_params(OakCurrent self, void **out);
+int oakcommon_current_get_audio_params(OakCurrent self, void **out);
+int oakcommon_current_get_plugin_host(OakCurrent self, void **out);
+int oakcommon_current_get_plugin_cache(OakCurrent self, void **out);
 
 /**
  * @brief Query whether the session is interactive.
  *
  * @param self Handle from oakcommon_current_instance().
  * @param out Receives 1 for interactive, 0 otherwise.
- * @return OAKCOMMON_OK on success, OAKCOMMON_E_INVALID if self or out
- * is NULL.
+ * @return OAKCOMMON_OK on success, OAKCOMMON_E_INVALID if self.ctx or
+ * out is NULL.
  */
-int oakcommon_current_is_interactive(OakCommonCurrent *self, int *out);
+int oakcommon_current_is_interactive(OakCurrent self, int *out);
 
 #ifdef __cplusplus
 }