Enable changing route providers after initializing a FerrostarCore instance

Discussing with a developer using Ferrostar, they expressed frustration that they had to create a new instance of `FerrostarCore` for every mode of travel their app supported.

A possible solution for this is to have an overload to `startNavigation` which lets you set a new profile / route adapter. We cannot make this a settable property at any other point in the flow safely though, because this would create very bad surprises during recalculation.

Start by reading the FerrostarCore lifecycle and the startNavigation entry point mentioned in the issue. Determine how a profile or route adapter can be selected when navigation starts without allowing unsafe changes during recalculation; done means one initialized core can support different travel modes safely.

Written by the indexing model from the issue text.