metrics: pull library and introduce ResettingTimer and InfluxDB reporter (#15910)

* go-metrics: fork library and introduce ResettingTimer and InfluxDB reporter.

* vendor: change nonsense/go-metrics to ethersphere/go-metrics

* go-metrics: add tests. move ResettingTimer logic from reporter to type.

* all, metrics: pull in metrics package in go-ethereum

* metrics/test: make sure metrics are enabled for tests

* metrics: apply gosimple rules

* metrics/exp, internal/debug: init expvar endpoint when starting pprof server

* internal/debug: tiny comment formatting fix

metrics/counter_test.go

@@ -0,0 +1,77 @@
+package metrics
+
+import "testing"
+
+func BenchmarkCounter(b *testing.B) {
+	c := NewCounter()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		c.Inc(1)
+	}
+}
+
+func TestCounterClear(t *testing.T) {
+	c := NewCounter()
+	c.Inc(1)
+	c.Clear()
+	if count := c.Count(); 0 != count {
+		t.Errorf("c.Count(): 0 != %v\n", count)
+	}
+}
+
+func TestCounterDec1(t *testing.T) {
+	c := NewCounter()
+	c.Dec(1)
+	if count := c.Count(); -1 != count {
+		t.Errorf("c.Count(): -1 != %v\n", count)
+	}
+}
+
+func TestCounterDec2(t *testing.T) {
+	c := NewCounter()
+	c.Dec(2)
+	if count := c.Count(); -2 != count {
+		t.Errorf("c.Count(): -2 != %v\n", count)
+	}
+}
+
+func TestCounterInc1(t *testing.T) {
+	c := NewCounter()
+	c.Inc(1)
+	if count := c.Count(); 1 != count {
+		t.Errorf("c.Count(): 1 != %v\n", count)
+	}
+}
+
+func TestCounterInc2(t *testing.T) {
+	c := NewCounter()
+	c.Inc(2)
+	if count := c.Count(); 2 != count {
+		t.Errorf("c.Count(): 2 != %v\n", count)
+	}
+}
+
+func TestCounterSnapshot(t *testing.T) {
+	c := NewCounter()
+	c.Inc(1)
+	snapshot := c.Snapshot()
+	c.Inc(1)
+	if count := snapshot.Count(); 1 != count {
+		t.Errorf("c.Count(): 1 != %v\n", count)
+	}
+}
+
+func TestCounterZero(t *testing.T) {
+	c := NewCounter()
+	if count := c.Count(); 0 != count {
+		t.Errorf("c.Count(): 0 != %v\n", count)
+	}
+}
+
+func TestGetOrRegisterCounter(t *testing.T) {
+	r := NewRegistry()
+	NewRegisteredCounter("foo", r).Inc(47)
+	if c := GetOrRegisterCounter("foo", r); 47 != c.Count() {
+		t.Fatal(c)
+	}
+}