refactor(undo): switch oakundo to refcounted value handles, migrate consumers

- OakUndoCommand/OakUndoStack become neutral by-value handles
  {ctx, addref, release, abi_version}; a handle is a shared_ptr
  equivalent at the ABI level, internals untouched (box owns/observes
  flag; containers adopt, boxes created by factories own)
- oaknode command factories and undoable variants return/write value
  handles; timeline command classes hold value handles; task import
  take_command returns a value handle
- tests updated everywhere; suites green: oakundo 22, oaktimeline 117,
  oaktask 106, oaknode 96, oakrender 44, oakcodec 18, oakcommon 193,
  oakaudio 36

src/timeline/c_api/workarea.cpp

@@ -39,16 +39,12 @@ const olive::TimelineWorkArea *impl(const OakTimelineWorkArea *h)
 	return reinterpret_cast<const olive::TimelineWorkArea *>(h);
 }
 
-OakUndoCommand *wrap_command(olive::UndoCommand *command)
+OakUndoCommand wrap_command(olive::UndoCommand *command)
 {
 	if (!command) {
-		return NULL;
+		return OakUndoCommand{};
 	}
-	OakUndoCommand *handle = new (std::nothrow) OakUndoCommand{command, true};
-	if (!handle) {
-		delete command;
-	}
-	return handle;
+	return oakundo_capi::make_command_handle(command, true);
 }
 
 olive::core::Rational rat(int64_t n, int64_t d)
@@ -113,13 +109,13 @@ int oaktimeline_workarea_set_range(OakTimelineWorkArea *w, int in_num,
 	}
 }
 
-OakUndoCommand *oaktimeline_workarea_set_range_command(
+OakUndoCommand oaktimeline_workarea_set_range_command(
 	OakTimelineWorkArea *w, int in_num, int in_den, int out_num,
 	int out_den, int old_in_num, int old_in_den, int old_out_num,
 	int old_out_den)
 {
 	if (!w) {
-		return NULL;
+		return OakUndoCommand{};
 	}
 
 	try {
@@ -129,22 +125,22 @@ OakUndoCommand *oaktimeline_workarea_set_range_command(
 		return wrap_command(
 			new olive::WorkareaSetRangeCommand(impl(w), range, old_range));
 	} catch (...) {
-		return NULL;
+		return OakUndoCommand{};
 	}
 }
 
-OakUndoCommand *oaktimeline_workarea_set_enabled_command(
+OakUndoCommand oaktimeline_workarea_set_enabled_command(
 	OakTimelineWorkArea *w, int enabled)
 {
 	if (!w) {
-		return NULL;
+		return OakUndoCommand{};
 	}
 
 	try {
 		return wrap_command(
 			new olive::WorkareaSetEnabledCommand(impl(w), enabled != 0));
 	} catch (...) {
-		return NULL;
+		return OakUndoCommand{};
 	}
 }