Sans-IO Low-Latency HLS (RFC 8216bis) client + server engines in one crate, mirroring rtsp-runtime's client+server split. `client`: a caller-driven blocking-reload scheduler, part-prefetch fetch pipeline, and ordered init+access-unit output, reusing transmux::hls for playlist parse and transmux::Fmp4Demux for CMAF->Sample decode, plus an optional tokio+reqwest async IO adapter. `server` (feature `std`): the sans-IO LL-HLS origin engine (rolling window/store, blocking-reload + part-availability decision logic, playlist rendering) an async adapter (e.g. multimux) drives. Zero IO deps in the client core. Renamed from `ll-hls-client` (never published).