pkg/util/metric: make v22.2 linter happy

The v22.2 backport of #96029
experienced some linter issues that didn't occur in the original patch.

This patch fixes those linter errors.

Release note: none

pkg/util/metric/hdrhistogram.go

@@ -226,20 +226,24 @@ func (h *HdrHistogram) GetMetadata() Metadata {
 	return baseMetadata
 }
 
+// ValueAtQuantileWindowed calculates the windowed quantile value for
+// this HdrHistogram.
 func (h *HdrHistogram) ValueAtQuantileWindowed(q float64) float64 {
 	h.mu.Lock()
 	defer h.mu.Unlock()
 
 	return ValueAtQuantileWindowed(h.toPrometheusMetricWindowedLocked().Histogram, q)
 }
 
+// Mean calculates the cumulative mean value for this HdrHistogram.
 func (h *HdrHistogram) Mean() float64 {
 	h.mu.Lock()
 	defer h.mu.Unlock()
 
 	return h.mu.cumulative.Mean()
 }
 
+// TotalSum calculates the cumulative sample sum value for this HdrHistogram.
 func (h *HdrHistogram) TotalSum() float64 {
 	h.mu.Lock()
 	defer h.mu.Unlock()

pkg/util/metric/metric.go

@@ -193,6 +193,8 @@ func HdrEnabled() bool {
 	return hdrEnabled
 }
 
+// HistogramMode specifies which type of histogram should be preferred
+// under various circumstances. See various constants for details.
 type HistogramMode byte
 
 const (
@@ -215,6 +217,8 @@ const (
 	HistogramModePreferHdrLatency
 )
 
+// HistogramOptions offers various configuration options available when
+// creating a new Histogram.
 type HistogramOptions struct {
 	// Metadata is the metric Metadata associated with the histogram.
 	Metadata Metadata
@@ -235,16 +239,17 @@ type HistogramOptions struct {
 	Mode HistogramMode
 }
 
+// NewHistogram creates a new IHistogram. The returned type is determined
+// based on the provided HistogramOptions, and/or the value of the
+// useHdrHistogramsEnvVar environment variable.
 func NewHistogram(opt HistogramOptions) IHistogram {
 	if hdrEnabled && opt.Mode != HistogramModePrometheus {
 		if opt.Mode == HistogramModePreferHdrLatency {
 			return NewHdrLatency(opt.Metadata, opt.Duration)
-		} else {
-			return NewHdrHistogram(opt.Metadata, opt.Duration, opt.MaxVal, opt.SigFigs)
 		}
-	} else {
-		return newHistogram(opt.Metadata, opt.Duration, opt.Buckets)
+		return NewHdrHistogram(opt.Metadata, opt.Duration, opt.MaxVal, opt.SigFigs)
 	}
+	return newHistogram(opt.Metadata, opt.Duration, opt.Buckets)
 }
 
 // NewHistogram is a prometheus-backed histogram. Depending on the value of
@@ -307,6 +312,8 @@ type Histogram struct {
 	}
 }
 
+// IHistogram is the interface that all core histogram
+// implementations should adhere to.
 type IHistogram interface {
 	Iterable
 	PrometheusExportable