Add SHM_LOCK_DIR environment variable for containerized deployments (memory leak fix)

[wes4m]

Problem

OSRM crashes with "lock file does not exist" when using shared memory (osrm-routed -s) in containerized environments (Kubernetes) after a container restart.

The crash triggers a restart/crash loop, and each restart accumulates orphaned shm segments, leaking memory proportional to the graph size until the node is exhausted.

Related issues: #5134, #5703

Reproduction

See gist: https://gist.github.com/wes4m/719cb69b72e26c09c7ff57ed71cf33d9

Why This Happens in Containers

OSRM's shared memory implementation assumes /tmp and System V shared memory have the same lifecycle. This is true on traditional systems where both are cleared on reboot, but not in containers:

Component	Traditional System	Container
/tmp filesystem	Cleared on reboot	Cleared on container restart
System V shared memory	Cleared on reboot	Survives container restart (IPC namespace persists)

When a container restarts:

1. /tmp is reset and lock files get deleted
2. IPC namespace survives with shm segments persisting (regardless of hostIPC setting)
3. SharedRegionRegister (in shm) still references old segments
4. OSRM checks for the old segment's lock file before attaching, doesn't find it, and crashes

Solution

This PR adds OSRM_LOCK_DIR environment variable to specify a custom directory for lock files. This allows containerized deployments to place lock files in a volume that persists across container restarts (e.g. kubernetes emptyDir)

Other Approaches

Mounting /tmp to a persistent volume fixes the issue but will persist all temporary files from the container, not just lock files. Setting TMPDIR will do the same, and cleaning orphaned shm segments on startup is a workaround that doesn't address the root cause.

OSRM_LOCK_DIR only affects lock file location and is backward compatible (tmp dir fallback), behavior is unchanged.

[TheMarex]

This change makes sense. Please add an entry to the changelog. Let me know if you have time to do the small edits yourself, otherwise I can try to put this on my TODO for the week.

[wes4m]

This change makes sense. Please add an entry to the changelog. Let me know if you have time to do the small edits yourself, otherwise I can try to put this on my TODO for the week.

Thanks for the review @TheMarex. changes pushed.