Interval: update equality checks

Since we are using floats, values should be tested with Float.compare.
Fusion: refine boundary iteration

This change updates the overlapping tile computation so that if, when
moving borders, an invalid tile is created it is discarded.

If the tile is still valid, it is adjusted a much smaller amount to
attempt to avoid breaking overlap with other tiles.
Fusion: add TODO

add notes for further fixing border calculation.