Pyramm

- Improve chainage layer builder

- fix bug in combine continuous segments

- add function to combine consecutive road segments

- fix issue where cache files fail to load

- improve centreline caching when building a partial centreline

- Add support for partial centrelines. This replaces the `road_id` argument in the `Centreline.displacement()` method that previously limited the map matching to the specified road_id.
- Change the `Centreline.displacement()` method to the `Centreline.position()` method and change the returned result to a dictionary.