This PR adds `v0318`, which is just like `v0316` but with bigger blocks.
It seems to perform best so far.

It also adds heuristics to avoid placing the marker token on closing
braces, which results in much nicer blocks.

Finally, it fixes a bug with inserting `<|marker_N|>` mid-line in
`v0316` and `v0317`.



Release Notes:

- N/A