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/StellaOps.Cryptography/GostSignatureFormat.cs

@@ -0,0 +1,13 @@
+namespace StellaOps.Cryptography;
+
+/// <summary>
+/// Desired wire format for GOST 34.10 signatures.
+/// </summary>
+public enum GostSignatureFormat
+{
+    /// <summary>DER-encoded ASN.1 sequence (default).</summary>
+    Der = 0,
+
+    /// <summary>Concatenated (s || r) raw bytes per RFC 9215.</summary>
+    Raw = 1
+}