refactor(render,timeline,task): switch remaining handles to refcounted value structs

- oakrender: renderer/texture/frame/cache/colorprocessor/ticket/copier
  all become by-value {ctx, addref, release, abi_version} handles over a
  generic box; retain() folds into addref; new
  oakrender_cache_wrap_borrowed for native caches from oaknode
- oaktimeline: marker list/workarea borrowed handles become value
  handles (non-owning boxes) with explicit free
- oaktask: OakTaskTask becomes a value handle; ownership still moves
  to the manager on start (owns flag flips)
- consumers (timeline/task/codec sources) migrated; tests everywhere
  updated; suites green: render 45, timeline 117, task 106, node 96,
  common 193, codec 18, audio 36

include/task/error.h

@@ -29,6 +29,8 @@
  * failure. String getters return the required buffer size in bytes
  * (including the terminating NUL) as a non-negative value instead.
  */
+#define OAKTASK_ABI_VERSION 1
+
 #define OAKTASK_OK 0 /**< Success. */
 #define OAKTASK_E_INVALID (-1) /**< NULL handle or invalid argument. */
 #define OAKTASK_E_STATE (-2) /**< Call not valid in the current state. */