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

src/render/tests/manager_test.cpp

@@ -30,7 +30,7 @@
 namespace
 {
 
-void noop_frame_ready(OakCodecFrame *frame, int64_t ts, void *userdata)
+void noop_frame_ready(OakCodecFrame frame, int64_t ts, void *userdata)
 {
 	(void) frame;
 	(void) ts;
@@ -100,7 +100,7 @@ TEST(OakRenderManagerTest, CancelUnknownRequest)
 TEST(OakRenderManagerTest, CacherSettersRequireManager)
 {
 	EXPECT_EQ(oakrender_set_cacher_multicam(OakNodeNode{}), OAKRENDER_E_STATE);
-	EXPECT_EQ(oakrender_set_display_color_processor(nullptr),
+	EXPECT_EQ(oakrender_set_display_color_processor(OakColorProcessor{}),
 			  OAKRENDER_E_STATE);
 }