integration: scale remaining hardcoded timeouts and replace pingAllHelper

Apply CI-aware scaling to all remaining hardcoded timeouts:

- requireAllClientsOfflineStaged: scale the three internal stage
  timeouts (15s/20s/60s) with ScaledTimeout.
- validateReloginComplete: scale requireAllClientsOnline (120s)
  and requireAllClientsNetInfoAndDERP (3min) calls.
- WaitForTailscaleSyncPerUser callers in acl_test.go (3 sites, 60s).
- WaitForRunning callers in tags_test.go (10 sites): switch to
  PeerSyncTimeout() to match convention.
- WaitForRunning/WaitForPeers direct callers in route_test.go.
- requireAllClientsOnline callers in general_test.go and
  auth_key_test.go.

Replace pingAllHelper with assertPingAll/assertPingAllWithCollect:

- Wraps pings in EventuallyWithT so transient docker exec timeouts
  are retried instead of immediately failing the test.
- Timeout scales with the ping matrix size (2s per ping budget for
  2 full sweeps) so large tests get proportionally more time.
- Uses CollectT correctly, fixing the broken EventuallyWithT usage
  in TestEphemeral where the old t.Errorf bypassed CollectT.
- Follows the established assert*/assertWithCollect naming.

Updates #3125

integration/auth_oidc_test.go

@@ -78,8 +78,7 @@ func TestOIDCAuthenticationPingAll(t *testing.T) {
 		return x.String()
 	})
 
-	success := pingAllHelper(t, allClients, allAddrs)
-	t.Logf("%d successful pings out of %d", success, len(allClients)*len(allIps))
+	assertPingAll(t, allClients, allAddrs)
 
 	headscale, err := scenario.Headscale()
 	require.NoError(t, err)
@@ -189,8 +188,7 @@ func TestOIDCExpireNodesBasedOnTokenExpiry(t *testing.T) {
 		return x.String()
 	})
 
-	success := pingAllHelper(t, allClients, allAddrs)
-	t.Logf("%d successful pings out of %d (before expiry)", success, len(allClients)*len(allIps))
+	assertPingAll(t, allClients, allAddrs)
 
 	// Wait for OIDC token expiry and verify all nodes transition to NeedsLogin.
 	// We add extra time to account for:
@@ -452,8 +450,7 @@ func TestOIDCAuthenticationWithPKCE(t *testing.T) {
 		return x.String()
 	})
 
-	success := pingAllHelper(t, allClients, allAddrs)
-	t.Logf("%d successful pings out of %d", success, len(allClients)*len(allIps))
+	assertPingAll(t, allClients, allAddrs)
 }
 
 // TestOIDCReloginSameNodeNewUser tests the scenario where: