Debug tiles are missing rate attribute on edges

[danpat]

Now that we support #77 , we need to be able to visualize values for route debugging.

The debug tiles expose the following attributes for road segments:

• speed
• is_small
• datasource
• weight
• duration
• name

Missing from this list is rate, which is length / weight. We have weight, but we have no normalize value (like `speed) that makes it easy to see where penalized weights are in play.

The task here is to add the rate attribute - it should be a simple duplication of how the speed is calculated and exposed.

[daniel-j-h]

Related: #3793

[daniel-j-h]

@danpat #4162 added rate to the debug tiles; anything left here that you want to add? Can you update your comment or close here please.

[danpat]

Ah, thanks for the reminder. This is done.