v0.17.13: thread Writer through patch + mux for big-write consistency

The bounded-cache writeback wrapper (crate::io::Writer) was added in
0.17.10 and wired into Disc::sweep in 0.17.11, but the other two
paths in the crate that write large amounts of data sequentially —
Disc::patch and the MKV/M2TS mux — were still operating on raw
std::fs::File. That meant the dirty-page burst pathology the wrapper
exists to prevent could still bite on slow / network-attached staging
during recovery and mux phases.

This release plugs those gaps:

- Disc::patch (disc/mod.rs:1981) now wraps the reopened ISO in
  Writer before any seek / write. sync_all on Writer cleanly drains
  the in-flight chunk before the existing fsync.
- mux/resolve.rs MKV and M2TS branches wrap the output File in
  Writer underneath BufWriter. UHD MKV mux routinely produces 70+ GB
  of sequential output; the page cache no longer absorbs that as a
  single hot blast on slow targets.

Mapfile, log, settings, history, and stream-pipeline byte buffers
remain unchanged: those are either small one-shot writes (where
the wrapper has zero benefit and adds a stream_position syscall) or
already use bounded persistence (mapfile time-batched in 0.17.12).
The principle: any path that writes substantial sequential data to
a single file uses Writer; trivial writes don't.

src/disc/mod.rs

@@ -1978,10 +1978,14 @@ impl Disc {
         let is_regular = std::fs::metadata(path)
             .map(|m| m.file_type().is_file())
             .unwrap_or(false);
-        let mut file = std::fs::OpenOptions::new()
+        let file = std::fs::OpenOptions::new()
             .write(true)
             .open(path)
             .map_err(|e| Error::IoError { source: e })?;
+        // Same bounded-cache writeback wrapper sweep uses, so patch's
+        // recovery writes (sparse but can be many across a damaged region)
+        // get the burst-flush protection on slow / NFS-backed staging.
+        let mut file = crate::io::Writer::new(file).map_err(|e| Error::IoError { source: e })?;
 
         // Log ISO file size at patch start for write monitoring
         if let Ok(metadata) = std::fs::metadata(path) {