addressed PR feedbacks

dart/lib/src/metrics/metric.dart

@@ -208,7 +208,7 @@ class SetMetric extends Metric {
       required super.unit,
       required super.tags})
       : super(type: MetricType.set) {
-    _values.add(value.toInt());
+    add(value);
   }
 
   @override
@@ -235,7 +235,7 @@ class DistributionMetric extends Metric {
       required super.unit,
       required super.tags})
       : super(type: MetricType.distribution) {
-    _values.add(value);
+    add(value);
   }
 
   @override

dart/lib/src/metrics/metrics_aggregator.dart

@@ -80,7 +80,7 @@ class MetricsAggregator {
     _scheduleFlush();
   }
 
-  Future<void> _scheduleFlush() async {
+  void _scheduleFlush() {
     if (!_isClosed && _buckets.isNotEmpty) {
       if (_isOverWeight()) {
         _flushTimer?.cancel();
@@ -133,7 +133,7 @@ class MetricsAggregator {
     _flushTimer = null;
     flushCompleter?.complete(null);
     _flushCompleter = null;
-    await _scheduleFlush();
+    _scheduleFlush();
   }
 
   /// Return a list of bucket keys to flush.

dart/lib/src/metrics/metrics_api.dart

@@ -10,6 +10,7 @@ class MetricsApi {
   final Hub _hub;
 
   /// Emits a Counter metric, identified by [key], increasing it by [value].
+  /// Counters track a value that can only be incremented.
   /// You can set the [unit] and the optional [tags] to associate to the metric.
   void increment(final String key,
       {final double value = 1.0,
@@ -25,6 +26,7 @@ class MetricsApi {
   }
 
   /// Emits a Gauge metric, identified by [key], adding [value] to it.
+  /// Gauges track a value that can go up and down.
   /// You can set the [unit] and the optional [tags] to associate to the metric.
   void gauge(final String key,
       {required final double value,
@@ -39,7 +41,8 @@ class MetricsApi {
     );
   }
 
-  /// Emits a Gauge metric, identified by [key], adding [value] to it.
+  /// Emits a Distribution metric, identified by [key], adding [value] to it.
+  /// Distributions track a list of values.
   /// You can set the [unit] and the optional [tags] to associate to the metric.
   void distribution(final String key,
       {required final double value,
@@ -57,6 +60,7 @@ class MetricsApi {
   /// Emits a Set metric, identified by [key], adding [value] or the CRC32
   ///  checksum of [stringValue] to it.
   /// Providing both [value] and [stringValue] adds both values to the metric.
+  /// Sets track a set of values to perform aggregations such as count_unique.
   /// You can set the [unit] and the optional [tags] to associate to the metric.
   void set(final String key,
       {final int? value,