Multidimensional metrics are sharing same reservoir when changed from default

[Rurouni]

Repro:

var services = new ServiceCollection();
services.AddLogging();
services.AddOptions();
services.AddMetrics();
var metrics = services.BuildServiceProvider().GetService<IMetrics>();

var timerDef = new TimerOptions()
{
    Reservoir = new Lazy<IReservoir>(() => new DefaultForwardDecayingReservoir())
};
var timer1 = metrics.Provider.Timer.Instance(timerDef, new MetricTags("test", "1"));
var timer2 = metrics.Provider.Timer.Instance(timerDef, new MetricTags("test", "2"));

timer1.Record(100, TimeUnit.Seconds);
timer1.Record(100, TimeUnit.Seconds);
timer1.Record(100, TimeUnit.Seconds);
timer1.Record(100, TimeUnit.Seconds);
timer1.Record(100, TimeUnit.Seconds);

var timers = metrics.Snapshot.Get().Contexts.First().Timers.ToArray();

Assert.Equal(5, timers[0].Value.Histogram.Count);
Assert.Equal(100_000, timers[0].Value.Histogram.Mean);

Assert.Equal(0, timers[1].Value.Histogram.Mean);
Assert.Equal(0, timers[1].Value.Histogram.Count);

Full project with that test:
AppMetricsBug.zip

[alhardy]

Passing test: d8433f5#diff-c0adf07e63a5b1bb37151239eee1d263R200