Fixes crashes in timeline and spreadsheet editors during simulation
nodes baking:
* Timeline tries to access the `states_at_frames_` list of the cache to
determine which frames to draw as baked. This can collide with the
baking thread. Needs a mutex to safely access the cache state.
Note: the old point cache has a pre-allocated flag array
`cached_frames` which the baking thread writes into while timeline is
reading it concurrently - not thread-safe but harmless.
* Spreadsheet keeps a data pointer during drawing, which may become
deallocated when the cache is updated. Common approach here is to use
`G.is_rendering` to lock the editor while baking.
Pull Request: https://projects.blender.org/blender/blender/pulls/107621
304e8a842d