* create a new type for crypto stream used for Initial data
This currently the exact same implementation as the other
streams, thus no functional change is expected.
* handshake: implement a function to find the SNI and the ECH extension
* move the SNI parsing logic to the quic package
* implement splitting logic
* generalize cutting logic
* introduce QUIC_GO_DISABLE_CLIENTHELLO_SCRAMBLING
* improve testing
