refactor(node,render): route oaknode->oakrender calls through the C ABI

- oakrender cache C API: add create_for_node (four cache kinds),
  get_uuid, request, load/save_state, set_saving_enabled,
  set_passthrough, get_passthroughs, get_valid_cache_filename,
  get_timebase, lock/unlock, invalidate_range (rational variant),
  get_native (C++ only, for the in-module PreviewAutoCacher)
- Node's four caches become owned OakRenderCache value handles; all
  cache access in node.cpp/clip/viewer/traverser/serializers goes
  through the C ABI
- oaknode_node_get_video_frame_cache returns an addref'd
  OakRenderCache; drop OakNodeFrameCache; oaktask precache/export and
  oakrender_video_ticket_params take the value handle
- color: OCIOBaseNode/OCIOLutNode hold OakColorProcessor handles
  (dtors added); oakrender gains color_processor_create_transform/
  create_lut/create_grading_primary/get_native and LUT library
  queries, keeping all OCIO transform construction inside oakrender;
  oaknode gains colormanager_wrap_borrowed/get_native
- RenderManager::instance() check -> oakrender_manager_available();
  cancel_video_tasks and disk cache path go through manager C API
- remaining node->render C++ symbol: only olive::Texture::~Texture
  via Variant's shared_ptr payload (recorded exception, same class as
  the UndoCommand inheritance)

Tests: new cache/color/manager/colormanager cases; all standalone
trees green (common 196, codec 22, audio 40, task 112, render 63,
timeline 125, node 98, plugin 102).

include/render/manager.h

@@ -120,6 +120,20 @@ int oakrender_set_cacher_multicam(OakNodeNode multicam_or_NULL);
  */
 int oakrender_set_display_color_processor(OakColorProcessor p_or_NULL);
 
+/**
+ * @brief 1 when the process-wide RenderManager singleton exists
+ *        (RenderManager::instance() != nullptr; only the main GUI
+ *        process creates one), 0 otherwise.
+ */
+int oakrender_manager_available(void);
+
+/**
+ * @brief Cancel in-flight video cache tasks on the manager's
+ *        auto-cacher (PreviewAutoCacher::cancel_video_tasks()). No-op
+ *        when no manager/auto-cacher exists (e.g. a worker process).
+ */
+void oakrender_cancel_video_tasks(int wait_for_done);
+
 /* ---- Disk cache (olive::DiskManager) -------------------------------------- */
 
 /**