cryptographic primitives (#118)

* AES-GSM encryption with padding

* RSA-OAEP encryption and key generation

* SPKI encoding/decoding RSA public keys

* rename functions

* encode/decode RSA keys using asn1lib library

* remove poitycastle namespace

* remove unnecessary typecheck

* fix: ci

Co-authored-by: alex <alex@tekartik.com>

packages/simplexmq/example/simplexmq_example.dart

@@ -1,6 +1 @@
-// import 'package:simplexmq/simplexmq.dart';
 
-// void main() {
-//   var awesome = Awesome();
-//   print('awesome: ${awesome.isAwesome}');
-// }