eth/tracers: fix evm trace for t8n (#34862)

The mux tracer fanned out every standard hook to its children but never
forwarded OnSystemCall{Start,End}. Tracers that rely on these - like
`logger.jsonLogger`, which uses the start hook to silence its opcode
hook for the duration of a system call - never got the signal when
wrapped behind a mux.

In evm t8n, combining `--trace` with `--opcode-count` (default for geth
with exec specs) produces exactly that wrapping. The first system call
(e.g. `ProcessBeaconBlockRoot`) then fires `OnOpcode` on the json logger
before any `OnTxStart` has run, dereferencing a nil env and crashing
t8n.

Forward both hooks through the mux. The V2 fan-out falls back to V1 for
children that only implement the legacy hook, mirroring the precedence
already used in `core/state_processor.go`.

eth/tracers/native/mux.go

@@ -79,6 +79,8 @@ func NewMuxTracer(names []string, objects []*tracers.Tracer) (*tracers.Tracer, e
 			OnCodeChange:        t.OnCodeChange,
 			OnStorageChange:     t.OnStorageChange,
 			OnLog:               t.OnLog,
+			OnSystemCallStartV2: t.OnSystemCallStart,
+			OnSystemCallEnd:     t.OnSystemCallEnd,
 		},
 		GetResult: t.GetResult,
 		Stop:      t.Stop,
@@ -189,6 +191,24 @@ func (t *muxTracer) OnLog(log *types.Log) {
 	}
 }
 
+func (t *muxTracer) OnSystemCallStart(vm *tracing.VMContext) {
+	for _, t := range t.tracers {
+		if t.OnSystemCallStartV2 != nil {
+			t.OnSystemCallStartV2(vm)
+		} else if t.OnSystemCallStart != nil {
+			t.OnSystemCallStart()
+		}
+	}
+}
+
+func (t *muxTracer) OnSystemCallEnd() {
+	for _, t := range t.tracers {
+		if t.OnSystemCallEnd != nil {
+			t.OnSystemCallEnd()
+		}
+	}
+}
+
 // GetResult returns an empty json object.
 func (t *muxTracer) GetResult() (json.RawMessage, error) {
 	resObject := make(map[string]json.RawMessage)