Create jittered route networks

I've extracted OSM road data for cycling and driving, but I haven't been able to use this yet for a jittered route network due to the following error:
```
> od_car_jittered = odjitter::jitter(
+ od = lines_car,
+ zones = tyneandwear,
+ zone_name_key = "geo_code",
+ subpoints_origins = osm_drive,
+ disaggregation_threshold = disag_threshold,
+ disaggregation_key = "car_driver",
+ min_distance_meters = min_distance_meters
+ )
Error in UseMethod("st_write") :
no applicable method for 'st_write' applied to an object of class "NULL"
```

Start by reproducing the odjitter::jitter call with the shown OSM, zone, and OD inputs, then trace why st_write receives NULL. There are no files or tests named in the issue; done means the cycling or driving route network is created without the reported error.

Written by the indexing model from the issue text.