narrow leaked-internal pub surface to pub(crate)

Verified zero callers across all consumer crates AND libfreemkv integration tests:
MUX_APP, Disc::{aacs_disc_hash,encrypted_content_ranges,inject_unit_keys},
locate_ranges, mapfile::{MapEntry,entries}, diag::dump_mkv_track,
DiscStream::{errors,lost_bytes} (read via accessors). Removed the unused mux
DemuxSink/FviSink crate-root re-exports (constructed internally by output() via
the direct module path). Staged demux option variants marked allow(dead_code).

src/mux/mod.rs

@@ -108,9 +108,10 @@ pub(crate) mod tsmux;
 #[allow(dead_code)]
 pub(crate) mod videomap;
 
-pub use demux_sink::{ChaptersFmt, DelayMode, DemuxOptions, DemuxSink, Naming};
+// `demux://` and `fvi://` sinks are constructed internally by `output()` via the
+// direct `super::demux_sink::` / `super::fvi_sink::` paths — no re-export needed,
+// and no consumer names these types, so they are not public API.
 pub use disc::DiscStream;
-pub use fvi_sink::FviSink;
 pub use m2ts::M2tsStream;
 pub use mkvstream::MkvStream;
 pub use network::NetworkStream;