Make the edge cost function less bad

[dabreegster]

https://github.com/dabreegster/routing-engines/blob/main/src/plugins/route_cost.rs is a placeholder

• A speed per way (so cobblestone or canal towpaths aren't fast, even if they're safe from LTS perspective)
• Can we directly or indirectly use profiles from OSRM, etc in a very quick way?