Add support for ГОСТ Р 34.10 digital signatures

- Implemented the GostKeyValue class for handling public key parameters in ГОСТ Р 34.10 digital signatures.
- Created the GostSignedXml class to manage XML signatures using ГОСТ 34.10, including methods for computing and checking signatures.
- Developed the GostSignedXmlImpl class to encapsulate the signature computation logic and public key retrieval.
- Added specific key value classes for ГОСТ Р 34.10-2001, ГОСТ Р 34.10-2012/256, and ГОСТ Р 34.10-2012/512 to support different signature algorithms.
- Ensured compatibility with existing XML signature standards while integrating ГОСТ cryptography.

src/__Libraries/__Tests/StellaOps.Cryptography.Tests/CryptoProGostSignerTests.cs

@@ -0,0 +1,41 @@
+#if STELLAOPS_CRYPTO_PRO
+using System;
+using System.Security.Cryptography;
+using System.Security.Cryptography.X509Certificates;
+using Microsoft.IdentityModel.Tokens;
+using StellaOps.Cryptography;
+using StellaOps.Cryptography.Plugin.CryptoPro;
+using Xunit;
+
+namespace StellaOps.Cryptography.Tests;
+
+public class CryptoProGostSignerTests
+{
+    [Fact]
+    public void ExportPublicJsonWebKey_ContainsCertificateChain()
+    {
+        using var ecdsa = ECDsa.Create(ECCurve.NamedCurves.nistP256);
+        var request = new CertificateRequest("CN=stellaops.test", ecdsa, HashAlgorithmName.SHA256);
+        using var cert = request.CreateSelfSigned(DateTimeOffset.UtcNow.AddDays(-1), DateTimeOffset.UtcNow.AddDays(1));
+
+        var entry = new CryptoProGostKeyEntry(
+            "test-key",
+            SignatureAlgorithms.GostR3410_2012_256,
+            cert,
+            "provider",
+            containerName: null,
+            useMachineKeyStore: false,
+            signatureFormat: GostSignatureFormat.Der);
+
+        var signer = new CryptoProGostSigner(entry);
+
+        var jwk = signer.ExportPublicJsonWebKey();
+
+        Assert.Equal("test-key", jwk.Kid);
+        Assert.Equal(SignatureAlgorithms.GostR3410_2012_256, jwk.Alg);
+        Assert.Equal(JsonWebKeyUseNames.Sig, jwk.Use);
+        Assert.Single(jwk.X5c);
+        Assert.Equal("EC", jwk.Kty);
+    }
+}
+#endif