feat: add strongly typed exceptions for retrieval failures

src/StevanFreeborn.Atproto.IdentityResolver/Exceptions/DidDocumentNotFoundException.cs

@@ -0,0 +1,28 @@
+namespace StevanFreeborn.Atproto.IdentityResolver.Exceptions;
+
+/// <summary>
+///
+/// </summary>
+public class DidDocumentNotFoundException : Exception
+{
+  /// <summary>
+  ///
+  /// </summary>
+  public DidDocumentNotFoundException()
+  {
+  }
+
+  /// <summary>
+  ///
+  /// </summary>
+  public DidDocumentNotFoundException(string message) : base(message)
+  {
+  }
+
+  /// <summary>
+  ///
+  /// </summary>
+  public DidDocumentNotFoundException(string message, Exception innerException) : base(message, innerException)
+  {
+  }
+}

src/StevanFreeborn.Atproto.IdentityResolver/Exceptions/DidNotFoundException.cs

@@ -0,0 +1,28 @@
+namespace StevanFreeborn.Atproto.IdentityResolver.Exceptions;
+
+/// <summary>
+///
+/// </summary>
+public class DidNotFoundException : Exception
+{
+  /// <summary>
+  ///
+  /// </summary>
+  public DidNotFoundException()
+  {
+  }
+
+  /// <summary>
+  ///
+  /// </summary>
+  public DidNotFoundException(string message) : base(message)
+  {
+  }
+
+  /// <summary>
+  ///
+  /// </summary>
+  public DidNotFoundException(string message, Exception innerException) : base(message, innerException)
+  {
+  }
+}