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

shared/include/oakutil/oakvideo.h

@@ -21,7 +21,7 @@
 #ifndef OAKUTIL_OAKVIDEO_H
 #define OAKUTIL_OAKVIDEO_H
 
-#include <QString>
+#include <string>
 
 #include <olive/core/util/rational.h>
 
@@ -167,30 +167,30 @@ class ColorTransform
 public:
 	ColorTransform() = default;
 
-	ColorTransform(const QString &output) : output_(output) {}
+	ColorTransform(const std::string &output) : output_(output) {}
 
-	ColorTransform(const QString &display, const QString &view,
-				   const QString &look)
+	ColorTransform(const std::string &display, const std::string &view,
+				   const std::string &look)
 		: output_(display), is_display_(true), view_(view), look_(look)
 	{
 	}
 
 	bool is_display() const { return is_display_; }
 
-	const QString &display() const { return output_; }
+	const std::string &display() const { return output_; }
 
-	const QString &output() const { return output_; }
+	const std::string &output() const { return output_; }
 
-	const QString &view() const { return view_; }
+	const std::string &view() const { return view_; }
 
-	const QString &look() const { return look_; }
+	const std::string &look() const { return look_; }
 
 private:
-	QString output_;
+	std::string output_;
 
 	bool is_display_ = false;
-	QString view_;
-	QString look_;
+	std::string view_;
+	std::string look_;
 };
 
 } // namespace oak