Move codec_privates onto DiscTitle, eliminate duplicate methods

Design fix: codec_privates are now a field on DiscTitle, not a separate
parameter passed through the pipeline. This eliminates the root cause of
the network codec_private bug (forgot to pass the separate param).

API changes:
- output() takes (url, &DiscTitle) — no separate codec_privates param
- MkvOutputStream::create, M2tsOutputStream::create, NetworkOutputStream::connect
  all read codec_privates from title.codec_privates
- M2tsMeta::from_title() takes only &DiscTitle — reads privates from title
- Deleted from_title_with_privates (was the wrong-name duplicate)
- Merged read_header + read_header_from_stream into one read_header(impl Read)
- Deleted finish(self) from TsMuxer, keep only finish(&mut self)

Rule: ONE public method per action. No _with_X, _from_Y, _ref variants.

src/mux/resolve.rs

@@ -370,7 +370,6 @@ pub fn input(url: &str, opts: &InputOptions) -> io::Result<Box<dyn crate::pes::S
 pub fn output(
     url: &str,
     title: &crate::disc::DiscTitle,
-    codec_privates: &[Option<Vec<u8>>],
 ) -> io::Result<Box<dyn crate::pes::Stream>> {
     let parsed = parse_url(url);
     match parsed {
@@ -380,11 +379,11 @@ pub fn output(
                 .map_err(|e| io::Error::new(e.kind(), format!("mkv://{}: {}", path.display(), e)))?;
             let writer: Box<dyn super::WriteSeek> =
                 Box::new(std::io::BufWriter::with_capacity(IO_BUF_SIZE, file));
-            Ok(Box::new(super::mkvout::MkvOutputStream::create(writer, title, codec_privates)?))
+            Ok(Box::new(super::mkvout::MkvOutputStream::create(writer, title)?))
         }
         StreamUrl::M2ts { ref path } => {
             validate_file_path(path, "m2ts")?;
-            Ok(Box::new(super::pesout::M2tsOutputStream::create(&path.to_string_lossy(), title, codec_privates)?))
+            Ok(Box::new(super::pesout::M2tsOutputStream::create(&path.to_string_lossy(), title)?))
         }
         StreamUrl::Network { ref addr } => {
             validate_network_addr(addr)?;