Add PositionCount property to Backtest models and responses

- Introduced PositionCount to Backtest, LightBacktest, and their respective response models.
- Updated BacktestController and BacktestExecutor to include PositionCount in responses.
- Modified database schema to accommodate new PositionCount field in relevant entities.

src/Managing.Infrastructure.Database/Migrations/20251118131323_AddPositionCountToBacktests.cs

@@ -0,0 +1,29 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Managing.Infrastructure.Databases.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddPositionCountToBacktests : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<int>(
+                name: "PositionCount",
+                table: "Backtests",
+                type: "integer",
+                nullable: false,
+                defaultValue: 0);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "PositionCount",
+                table: "Backtests");
+        }
+    }
+}

src/Managing.Infrastructure.Database/Migrations/ManagingDbContextModelSnapshot.cs

@@ -217,6 +217,9 @@ namespace Managing.Infrastructure.Databases.Migrations
                     b.Property<decimal>("NetPnl")
                         .HasColumnType("decimal(18,8)");
 
+                    b.Property<int>("PositionCount")
+                        .HasColumnType("integer");
+
                     b.Property<string>("PositionsJson")
                         .IsRequired()
                         .HasColumnType("jsonb");

src/Managing.Infrastructure.Database/PostgreSql/Entities/BacktestEntity.cs

@@ -128,4 +128,7 @@ public class BacktestEntity
     [Required]
     [Column(TypeName = "decimal(18,8)")]
     public decimal NetPnl { get; set; }
+
+    [Required]
+    public int PositionCount { get; set; }
 }