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/debug.h

@@ -32,7 +32,7 @@ extern "C" {
  *
  * Mirrors olive::DebugLevel in src/common/src/debug.h.
  */
-enum OakCommonDebugLevel {
+enum OakDebugLevel {
 	OAKCOMMON_DEBUG_DEBUG = 0, /**< Verbose debug message. */
 	OAKCOMMON_DEBUG_INFO = 1, /**< Informational message. */
 	OAKCOMMON_DEBUG_WARNING = 2, /**< Warning message. */
@@ -46,7 +46,7 @@ enum OakCommonDebugLevel {
  * De-Qt replacement for the old Qt message handler. The line is
  * flushed immediately.
  *
- * @param level One of OakCommonDebugLevel; out-of-range values print
+ * @param level One of OakDebugLevel; out-of-range values print
  * as "UNKNOWN".
  * @param msg NUL-terminated message; NULL is treated as an empty
  * string.
@@ -60,7 +60,7 @@ int oakcommon_debug_log(int level, const char *msg);
  * Two-segment string getter: if buf is NULL or buf_size is too small,
  * nothing is written.
  *
- * @param level One of OakCommonDebugLevel.
+ * @param level One of OakDebugLevel.
  * @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
@@ -68,6 +68,44 @@ int oakcommon_debug_log(int level, const char *msg);
  */
 int oakcommon_debug_level_name(int level, char *buf, int buf_size);
 
+/**
+ * @brief printf-style filtered log, replacing qDebug()/qInfo()/
+ * qWarning()/qCritical() call sites.
+ *
+ * The message is formatted with vsnprintf into a dynamically sized
+ * buffer (arbitrary length, no truncation, no fixed stack buffer) and
+ * emitted as "[LEVEL] message\n" unless @p level is below the current
+ * filter level (see oakcommon_log_set_level()).
+ *
+ * @param level One of OakDebugLevel; out-of-range values print
+ * as "UNKNOWN" and are never filtered out below FATAL.
+ * @param fmt printf-style format string. Must not be NULL.
+ * @return OAKCOMMON_OK on success, OAKCOMMON_E_INVALID if fmt is NULL,
+ *         OAKCOMMON_E_FAILED if formatting failed.
+ */
+int oakcommon_log(int level, const char *fmt, ...);
+
+/**
+ * @brief Set the minimum level emitted by oakcommon_log().
+ *
+ * Messages with a lower level are dropped. The default is
+ * OAKCOMMON_DEBUG_INFO.
+ *
+ * @param level One of OakDebugLevel.
+ * @return OAKCOMMON_OK on success, OAKCOMMON_E_INVALID if level is
+ *         outside the OakDebugLevel range.
+ */
+int oakcommon_log_set_level(int level);
+
+/**
+ * @brief Query the current minimum level emitted by oakcommon_log().
+ *
+ * @param out_level Receives one of OakDebugLevel. Must not be NULL.
+ * @return OAKCOMMON_OK on success, OAKCOMMON_E_INVALID if out_level is
+ *         NULL.
+ */
+int oakcommon_log_get_level(int *out_level);
+
 #ifdef __cplusplus
 }
 #endif