Deprecate repositories and update service interfaces

- Marked `IEnvelopeReceiverRepository` and several repository classes as obsolete, recommending the use of `IRepository`.
- Corrected `using` directive in `IReceiverService.cs`.
- Removed `UpdateAsync` method from `IReceiverService`.
- Enhanced `ISmsSender` interface with new properties and methods.
- Updated `ReceiverCreateDto`, `ReceiverReadDto`, and `UserReceiverDto` to enforce non-nullable properties.
- Refactored `TestReceiverController` to suggest using `MediatR`.

EnvelopeGenerator.Application/DTOs/Receiver/ReceiverCreateDto.cs

@@ -18,7 +18,7 @@ public record ReceiverCreateDto
     {
         _sha256HexOfMail = new(() =>
         {
-            var bytes_arr = Encoding.UTF8.GetBytes(EmailAddress.ToUpper());
+            var bytes_arr = Encoding.UTF8.GetBytes(EmailAddress!.ToUpper());
             var hash_arr = SHA256.HashData(bytes_arr);
             var hexa_str = BitConverter.ToString(hash_arr);
             return hexa_str.Replace("-", string.Empty);
@@ -37,7 +37,7 @@ public record ReceiverCreateDto
     public string? TotpSecretkey { get; init; }
 
     /// <summary>
-    /// var bytes_arr = Encoding.UTF8.GetBytes(EmailAddress.ToUpper());<br>
+    /// var bytes_arr = Encoding.UTF8.GetBytes(EmailAddress.ToUpper());<br/>
     /// var hash_arr = SHA256.HashData(bytes_arr);
     /// var hexa_str = BitConverter.ToString(hash_arr);
     /// return hexa_str.Replace("-", string.Empty);