Refactor DI extensions and add SQL executor support

Removed `DIExtensions.cs` and integrated its content into `DependencyExtensions.cs`, enhancing the dependency injection setup with repository and SQL executor registrations. Added a new `CreateEnvelopeSQL` class implementing the `ISQL<Envelope>` interface, currently with a placeholder implementation.

EnvelopeGenerator.Application/Envelopes/Commands/CreateEnvelopeSQL.cs

@@ -0,0 +1,14 @@
+using EnvelopeGenerator.Application.Contracts.SQLExecutor;
+using EnvelopeGenerator.Domain.Entities;
+
+namespace EnvelopeGenerator.Application.Envelopes.Commands;
+/// <summary>
+/// 
+/// </summary>
+public class CreateEnvelopeSQL : ISQL<Envelope>
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    public string Raw => string.Empty;
+}

EnvelopeGenerator.Infrastructure/DependencyExtensions.cs

@@ -6,6 +6,7 @@ using Microsoft.EntityFrameworkCore;
 using DigitalData.Core.Infrastructure;
 using EnvelopeGenerator.Domain.Entities;
 using DigitalData.Core.Infrastructure.AutoMapper;
+using EnvelopeGenerator.Application.Contracts.SQLExecutor;
 
 namespace EnvelopeGenerator.Infrastructure;
 
@@ -59,6 +60,42 @@ public static class DIExtensions
         services.AddDbRepository<EGDbContext, UserReceiver>(context => context.UserReceivers).UseAutoMapper();
         services.AddDbRepository<EGDbContext, EnvelopeReceiverReadOnly>(context => context.EnvelopeReceiverReadOnlys).UseAutoMapper();
 
+        services.AddSQLExecutor<Envelope>();
+        services.AddSQLExecutor<Receiver>();
+        services.AddSQLExecutor<EnvelopeDocument>();
+        services.AddSQLExecutor<DocumentReceiverElement>();
+        services.AddSQLExecutor<DocumentStatus>();
+
+        return services;
+    }
+
+    public static IServiceCollection AddSQLExecutor<T>(this IServiceCollection services) where T : class
+    {
+        services.AddSingleton<ISQLExecutor<T>, SQLExecutor<T>>();
+
+        var interfaceType = typeof(ISQL<>);
+        var targetGenericType = interfaceType.MakeGenericType(typeof(T));
+
+        var implementations = AppDomain.CurrentDomain.GetAssemblies()
+            .SelectMany(a =>
+            {
+                try { return a.GetTypes(); }
+                catch { return Array.Empty<Type>(); }
+            })
+            .Where(t =>
+                t is { IsClass: true, IsAbstract: false } &&
+                t.GetInterfaces().Any(i =>
+                    i.IsGenericType &&
+                    i.GetGenericTypeDefinition() == interfaceType &&
+                    i.GenericTypeArguments[0] == typeof(T)
+                )
+            );
+
+        foreach (var impl in implementations)
+        {
+            services.AddSingleton(impl);
+        }
+
         return services;
     }
 }