refactor+feat: Custom Client Handshake + Implement ALPS extension (#142)

* refactor: split `CompressCertExtension` changes

- Split most of changes for `CompressCertExtension` made to `crypto/tls` files out and moved them to `u_` files.
- Edited some `crypto/tls` files to achieve better programmability for uTLS.
- Minor styling fix.

* feat: implement ALPS Extension draft

- Made necessary modifications to existing types to support ALPS.
- Ported `ApplicationSettingsExtension` implementation from `ulixee/utls` by @blakebyrnes with some adaptation.

Co-Authored-By: Blake Byrnes <115056+blakebyrnes@users.noreply.github.com>

* feat: utlsFakeCustomExtension in ALPS

- Introducing `utlsFakeCustomExtension` to enable implementation for custom extensions to be exchanged via ALPS.
- currently it doesn't do anything.

Co-Authored-By: Blake Byrnes <115056+blakebyrnes@users.noreply.github.com>

* fix: magic number in `StatusRequestV2Extension`

- Fixed magic number `17` in `StatusRequestV2Extension` with pre-defined enum `extensionStatusRequestV2`.

Co-authored-by: Blake Byrnes <115056+blakebyrnes@users.noreply.github.com>

handshake_messages.go

@@ -868,6 +868,8 @@ func (m *serverHelloMsg) unmarshal(data []byte) bool {
 type encryptedExtensionsMsg struct {
 	raw          []byte
 	alpnProtocol string
+
+	utls utlsEncryptedExtensionsMsgExtraFields // [uTLS]
 }
 
 func (m *encryptedExtensionsMsg) marshal() []byte {
@@ -927,6 +929,11 @@ func (m *encryptedExtensionsMsg) unmarshal(data []byte) bool {
 			}
 			m.alpnProtocol = string(proto)
 		default:
+			// [UTLS SECTION START]
+			if !m.utlsUnmarshal(extension, extData) {
+				return false // return false when ERROR
+			}
+			// [UTLS SECTION END]
 			// Ignore unknown extensions.
 			continue
 		}