Replace AllocRatio ctor creation to the static field, like BaselineRatioColumn.RatioMean

Author: YegorStepanov

src/BenchmarkDotNet/Columns/BaselineAllocationRatioColumn.cs

@@ -14,6 +14,10 @@ public class BaselineAllocationRatioColumn : BaselineCustomColumn
         public override string Id => nameof(BaselineAllocationRatioColumn);
         public override string ColumnName => Column.AllocRatio;
 
+        public static readonly IColumn RatioMean = new BaselineAllocationRatioColumn();
+
+        private BaselineAllocationRatioColumn() { }
+
         public override string GetValue(Summary summary, BenchmarkCase benchmarkCase, Statistics baseline, IReadOnlyDictionary<string, Metric> baselineMetrics,
             Statistics current, IReadOnlyDictionary<string, Metric> currentMetrics, bool isBaseline)
         {

src/BenchmarkDotNet/Columns/DefaultColumnProvider.cs

@@ -66,7 +66,7 @@ public IEnumerable<IColumn> GetColumns(Summary summary)
 
                     if (HasMemoryDiagnoser(summary))
                     {
-                        yield return new BaselineAllocationRatioColumn();
+                        yield return BaselineAllocationRatioColumn.RatioMean;
                     }
                 }
             }