Reworked encryption to use less heap allocated buffers for secrets.

Also some work on plugin system.

IdentityShroud.Core/Security/Jwt/JwtSignerFactory.cs

@@ -0,0 +1,17 @@
+namespace IdentityShroud.Core;
+
+public class JwtSignerFactory(IEnumerable<IJwtSigner> signers) : IJwtSignerFactory
+{
+    private readonly IReadOnlyDictionary<JwtSigAlgName, IJwtSigner> _signers = signers
+        .SelectMany(s => s.Algorithms.Select(alg => (alg, signer: s)))
+        .ToDictionary(x => x.alg, x => x.signer);
+    
+    public IJwtSigner Create(JwtSigAlgName algorithm)
+    {
+        if (_signers.TryGetValue(algorithm, out var signer))
+            return signer;
+
+        throw new NotSupportedException($"JWT signing algorithm '{algorithm}' is not registered.");
+    }
+    
+}