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

vendor/github.com/influxdata/influxdb/models/inline_fnv.go

@@ -0,0 +1,32 @@
+package models // import "github.com/influxdata/influxdb/models"
+
+// from stdlib hash/fnv/fnv.go
+const (
+	prime64  = 1099511628211
+	offset64 = 14695981039346656037
+)
+
+// InlineFNV64a is an alloc-free port of the standard library's fnv64a.
+// See https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function.
+type InlineFNV64a uint64
+
+// NewInlineFNV64a returns a new instance of InlineFNV64a.
+func NewInlineFNV64a() InlineFNV64a {
+	return offset64
+}
+
+// Write adds data to the running hash.
+func (s *InlineFNV64a) Write(data []byte) (int, error) {
+	hash := uint64(*s)
+	for _, c := range data {
+		hash ^= uint64(c)
+		hash *= prime64
+	}
+	*s = InlineFNV64a(hash)
+	return len(data), nil
+}
+
+// Sum64 returns the uint64 of the current resulting hash.
+func (s *InlineFNV64a) Sum64() uint64 {
+	return uint64(*s)
+}