How does KIP-0021 prevent Kaspa node memory from growing without limit?

KIP-0021 keeps memory bounded by automatically purging lanes that have been inactive for too long, removing them from the network's active-lane registry. Every tracked lane in `ActiveLanes` carries a `last_touch_blue_score` — the blue score value at the most recent block where the lane was active. A protocol parameter called `F`, measured in blue score units, sets the inactivity threshold: once the current block's blue score equals or exceeds a lane's last recorded touch plus `F`, that lane is considered stale and is deleted from `ActiveLanes`. This matters for anyone running a Kaspa node because it guarantees the set of tracked lanes can never grow indefinitely — a hard requirement for a network designed to run at high block rates over a long time horizon.