Impossible/impracticable to undo automated filter placement in Design LTN tool

How to reproduce
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- In the Design LTN tool, select a large-ish neighbourhood
- Try automatically placing filters using the following option:

> Advanced -> Automatically place modal filters -> stop the most shortcuts (bute-force)

- Attempt to undo the placement of the filter

Expected behaviour
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The user should be able to undo the filter placement with a single undo.

Actual behaviour
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The user may need to select undo > 100 times in order to return to the state before automatically placing the filter.

(It seems that an edit is made and undone for each candidate filter (see https://github.com/a-b-street/abstreet/blob/70002600991c4611d3d905da59173c0b74cee2a6/apps/ltn/src/logic/auto_filters.rs#L105) (~= the number of interior roads in the neighbourhood). This can be > 100, making it impracticable for the user to undo this change later.