all: remove deprecated uses of math.rand (#26710)

This PR is a (superior) alternative to https://github.com/ethereum/go-ethereum/pull/26708, it handles deprecation, primarily two specific cases. 

`rand.Seed` is typically used in two ways
- `rand.Seed(time.Now().UnixNano())` -- we seed it, just to be sure to get some random, and not always get the same thing on every run. This is not needed, with global seeding, so those are just removed. 
- `rand.Seed(1)` this is typically done to ensure we have a stable test. If we rely on this, we need to fix up the tests to use a deterministic prng-source. A few occurrences like this has been replaced with a proper custom source. 

`rand.Read` has been replaced by `crypto/rand`.`Read` in this PR.

metrics/sample.go

@@ -41,6 +41,7 @@ type ExpDecaySample struct {
 	reservoirSize int
 	t0, t1        time.Time
 	values        *expDecaySampleHeap
+	rand          *rand.Rand
 }
 
 // NewExpDecaySample constructs a new exponentially-decaying sample with the
@@ -59,6 +60,12 @@ func NewExpDecaySample(reservoirSize int, alpha float64) Sample {
 	return s
 }
 
+// SetRand sets the random source (useful in tests)
+func (s *ExpDecaySample) SetRand(prng *rand.Rand) Sample {
+	s.rand = prng
+	return s
+}
+
 // Clear clears all samples.
 func (s *ExpDecaySample) Clear() {
 	s.mutex.Lock()
@@ -168,8 +175,14 @@ func (s *ExpDecaySample) update(t time.Time, v int64) {
 	if s.values.Size() == s.reservoirSize {
 		s.values.Pop()
 	}
+	var f64 float64
+	if s.rand != nil {
+		f64 = s.rand.Float64()
+	} else {
+		f64 = rand.Float64()
+	}
 	s.values.Push(expDecaySample{
-		k: math.Exp(t.Sub(s.t0).Seconds()*s.alpha) / rand.Float64(),
+		k: math.Exp(t.Sub(s.t0).Seconds()*s.alpha) / f64,
 		v: v,
 	})
 	if t.After(s.t1) {
@@ -402,6 +415,7 @@ type UniformSample struct {
 	mutex         sync.Mutex
 	reservoirSize int
 	values        []int64
+	rand          *rand.Rand
 }
 
 // NewUniformSample constructs a new uniform sample with the given reservoir
@@ -416,6 +430,12 @@ func NewUniformSample(reservoirSize int) Sample {
 	}
 }
 
+// SetRand sets the random source (useful in tests)
+func (s *UniformSample) SetRand(prng *rand.Rand) Sample {
+	s.rand = prng
+	return s
+}
+
 // Clear clears all samples.
 func (s *UniformSample) Clear() {
 	s.mutex.Lock()
@@ -511,7 +531,12 @@ func (s *UniformSample) Update(v int64) {
 	if len(s.values) < s.reservoirSize {
 		s.values = append(s.values, v)
 	} else {
-		r := rand.Int63n(s.count)
+		var r int64
+		if s.rand != nil {
+			r = s.rand.Int63n(s.count)
+		} else {
+			r = rand.Int63n(s.count)
+		}
 		if r < int64(len(s.values)) {
 			s.values[int(r)] = v
 		}