Infinite loop fix, API updates, QUICv2 fix, post-quantum fix
- Update to ls-qpack v2.6.1 to fix a infinite loop.
- Add lsquic_engine_get_conns_count() API
- Updated ea_generate_scid() API
- Fix retry packet SCID generation to follow the engine API.
- Fix QUICv2 header protection key when a retry packet is involved.