[DevTask] LGraph setDirtyCanvas

When items are added/removed, LGraph is setting the dirty canvas bit. This is fine for very simple operations, but does not scale when the UI scales in complexity.

If we want to ensure deleted items are also removed from selected items lists, that the canvas is redrawn, and all relevant callbacks are called, it becomes an issue: when removing 20 nodes, everything is run 20 times (including callbacks that should run on e.g. an array of results).

Either:
1. Add remove-many API
2. Ensure callers handle the pre/post remove operations, including dirty canvas.

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