refactor(BurnPdfCommand): add extension methods for ISender

- Introduce BurnPdfCommandExtensions to simplify sending BurnPdfCommand via ISender
- Enables calling `sender.BurnPdf(envelopeId, cancel)` or `sender.BurnPdf(envelopeUuid, cancel)`
- No changes to the underlying PDF burning logic in BurnPdfCommandHandler

EnvelopeGenerator.Application/Pdf/BurnPdfCommand.cs

@@ -20,6 +20,32 @@ namespace EnvelopeGenerator.Application.Pdf;
 /// </summary>
 public record BurnPdfCommand(int? EnvelopeId = null, string? EnvelopeUuid = null) : IRequest<byte[]>;
 
+/// <summary>
+/// 
+/// </summary>
+public static class BurnPdfCommandExtensions
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="sender"></param>
+    /// <param name="envelopeId"></param>
+    /// <param name="cancel"></param>
+    /// <returns></returns>
+    public static Task<byte[]> BurnPdf(this ISender sender, int envelopeId, CancellationToken cancel) 
+        => sender.Send(new BurnPdfCommand(EnvelopeId: envelopeId), cancel);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="sender"></param>
+    /// <param name="envelopeUuid"></param>
+    /// <param name="cancel"></param>
+    /// <returns></returns>
+    public static Task<byte[]> BurnPdf(this ISender sender, string envelopeUuid, CancellationToken cancel)
+        => sender.Send(new BurnPdfCommand(EnvelopeUuid: envelopeUuid), cancel);
+}
+
 /// <summary>
 /// 
 /// </summary>