Remove usage of Linq in Base62 encoding

Should be faster and cause fewer allocations

System/Base62.cs

@@ -24,7 +24,6 @@
 #endregion
 
 #nullable enable
-using System.Linq;
 using System.Numerics;
 using System.Text;
 
@@ -53,7 +52,11 @@ public static string Encode(BigInteger value)
                 value /= 62;
             }
 
-            return new string(sb.ToString().Reverse().ToArray());
+            // Reverse the string, since we're building it backwards, 
+            var chars = sb.ToString().ToCharArray();
+            Array.Reverse(chars);
+
+            return new string(chars);
         }
 
         /// <summary>
@@ -78,4 +81,4 @@ public static BigInteger Decode(string value)
             _ => throw new ArgumentException($"Cannot decode char '{c}' from base 62.", nameof(c)),
         };
     }
-}
+}