Slice 2/13. New impl QobuzClient block in qbz-qobuz/src/purchases.rs ported
1:1 from src-tauri api/client.rs: typed/ids purchase listing (page_limit 500,
two-call per-type totals quirk preserved), get_track_file_url_by_format
(RPC-signed, intent=stream, empty-url -> TrackUnavailable), and download_audio
(http1_only, NO total timeout). Adds 2 endpoint consts; bumps
http()/secret()/authenticated_headers() to pub(crate) for the sibling module.
Offline-gated via self.http()?. Drops .use_native_tls() (crates/ workspace is
rustls-only; matches cmaf.rs build_cdn_client) to keep the standalone build green.
cc
vicrodh
26b6480ff1