OSMNodeData stored barrier node tags in a List<Map<String,Object>>,
allocating a HashMap per tagged node. On a planet-scale import this
produces millions of short-lived hash maps, driving GC pause time and ballooning heap pressure throughout the read pass.

Backported KVStorage (com.graphhopper.search) to replace the list with a compact,
MMAP-backed byte store. Tags are serialised once and looked up by index,
eliminating per-node HashMap overhead entirely.

 When the fork is upgraded to a GH version that ships KVStorage natively, remove all
ORS-GH BACKPORT markers in OSMNodeData.java plus KVStorage.java and the
version constant.