add duration metric, tolerate missing tracepoints, ship el8 build

- Bubbles, treemap, icicle, and the live flamegraph 'b' cycle now include
  syscall duration (sum) as a third metric alongside events and bytes.
  Statsengine snapshots expose TotalLatencyNs to support this.
- AttachAll takes an optional warn callback. Production passes one so older
  kernels that lack newer tracepoints log a warning and keep going instead
  of aborting startup.
- Dockerfile.el8 + scripts/build-with-docker-el8.sh + mage buildDockerEl8
  produce ior.el8, a static binary built against Rocky Linux 8 glibc for
  RHEL/Rocky/Alma 8 hosts.
- README.md documents installing mage and the new el8 target.

1 files changed, 7 insertions, 6 deletions

diff --git a/internal/statsengine/process.go b/internal/statsengine/process.go
index 3bfd019..b7eb6e7 100644
--- a/internal/statsengine/process.go
+++ b/internal/statsengine/process.go
@@ -174,11 +174,12 @@ func (s processSnapshotInput) toSnapshot(rateDiv float64) ProcessSnapshot {
 	}
 
 	return ProcessSnapshot{
-		PID:          s.pid,
-		Comm:         s.comm,
-		Syscalls:     s.count,
-		RatePerSec:   safeRate(s.count, rateDiv),
-		Bytes:        s.totalBytes,
-		AvgLatencyNs: avg,
+		PID:            s.pid,
+		Comm:           s.comm,
+		Syscalls:       s.count,
+		RatePerSec:     safeRate(s.count, rateDiv),
+		Bytes:          s.totalBytes,
+		AvgLatencyNs:   avg,
+		TotalLatencyNs: s.totalLatency,
 	}
 }