* Xtls: code refactor
- Move more logic to VisionReader/Writer
- Remove XtlsWrite()
- XtlsRead now only handle splice at the outbound
- This helps VLESS inbound to have simple buf.copy() so that we can remove pipe next
* Add bufferFlushNext; Use DispatchLink() in VLESS inbound
* Use TimeoutWrapperReader; clean up timer/buffer
* Increase some tls test timeout
* Fix TestUserValidator
* Change all tests to VMessAEAD
Old VMess MD5 tests will be rejected and fail in 2022
* Chore: auto format code
