Refactor SQL execution classes into new namespace

Restructure and refactor classes related to SQL execution within the `EnvelopeGenerator.Infrastructure` namespace. Key changes include:
- Added `EnvelopeGenerator.Infrastructure.Executor` namespace.
- Moved and redefined `Query`, `QueryExtension`, `SQLExecutor`, `SQLExecutorBaseEntity`, and `SQLExecutorParams` classes to the new namespace.
- Maintained existing functionality while improving code organization and clarity.

EnvelopeGenerator.Infrastructure/Executor/Query.cs

@@ -0,0 +1,41 @@
+using EnvelopeGenerator.Application.Contracts.SQLExecutor;
+using Microsoft.EntityFrameworkCore;
+
+namespace EnvelopeGenerator.Infrastructure.Executor;
+
+public sealed record Query<TEntity> : IQuery<TEntity>
+{
+    private readonly IQueryable<TEntity> _query;
+
+    internal Query(IQueryable<TEntity> queryable)
+    {
+        _query = queryable;
+    }
+
+    public TEntity First() => _query.First();
+
+    public Task<TEntity> FirstAsync() => _query.FirstAsync();
+
+    public TEntity? FirstOrDefault() => _query.FirstOrDefault();
+
+
+    public Task<TEntity?> FirstOrDefaultAsync() => _query.FirstOrDefaultAsync();
+
+
+    public TEntity Single() => _query.Single();
+
+
+    public Task<TEntity> SingleAsync() => _query.SingleAsync();
+
+
+    public TEntity? SingleOrDefault() => _query.SingleOrDefault();
+
+
+    public Task<TEntity?> SingleOrDefaultAsync() => _query.SingleOrDefaultAsync();
+
+
+    public IEnumerable<TEntity> ToList() => _query.ToList();
+
+
+    public async Task<IEnumerable<TEntity>> ToListAsync() => await _query.ToListAsync();
+}