- oaktimeline::multicam: clip_find_multicam (buffer/tex_in depth-1
lookup), multicam_enable/disable (rewire sequence<->clip through a
MultiCamNode), multicam_switch (split-preserving-links at the
playhead, each half owns an independent multicam copy, linked clips
switched together) as single undo commands with C++ labels.
- BlockSplitCommand now duplicates the clip's whole dependency graph
(copy_node_and_dependency_graph_minus_items) instead of just the
block core, matching the C++ BlockSplitCommand::prepare semantics;
undo detaches the copied subgraph, redo re-attaches identity-
preserving.
- oaknode: fix serializer dropping edges from the first-created node
(ptr=0 was not registered in id_map), restoring sequence_in edge
round-trips; multicam node and clip wiring serializer round-trip
tests.