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, 10 insertions, 2 deletions

diff --git a/internal/tui/flamegraph/model_test.go b/internal/tui/flamegraph/model_test.go
index c2626cd..e864e88 100644
--- a/internal/tui/flamegraph/model_test.go
+++ b/internal/tui/flamegraph/model_test.go
@@ -987,12 +987,20 @@ func TestControlMetricToggleReconfiguresLiveTrieCountField(t *testing.T) {
 	}
 
 	m = pressFlameKey(t, m, tea.KeyPressMsg{Code: []rune{'b'}[0], Text: "b"})
-	if got, want := m.countField, "count"; got != want {
+	if got, want := m.countField, "duration"; got != want {
 		t.Fatalf("expected model count field %q after second toggle, got %q", want, got)
 	}
-	if got, want := liveTrie.CountField(), "count"; got != want {
+	if got, want := liveTrie.CountField(), "duration"; got != want {
 		t.Fatalf("expected live trie count field %q after second toggle, got %q", want, got)
 	}
+
+	m = pressFlameKey(t, m, tea.KeyPressMsg{Code: []rune{'b'}[0], Text: "b"})
+	if got, want := m.countField, "count"; got != want {
+		t.Fatalf("expected model count field %q after third toggle, got %q", want, got)
+	}
+	if got, want := liveTrie.CountField(), "count"; got != want {
+		t.Fatalf("expected live trie count field %q after third toggle, got %q", want, got)
+	}
 }
 
 func TestNewModelAlignsPresetIndexToLiveTrieFields(t *testing.T) {