v0.10.1: Streams are PES, Disc::copy() for sector dumps, zero English

Architecture:
- One stream per format, bidirectional PES (read/write on same type)
- IsoStream merged into DiscStream (one type, any SectorReader)
- Disc::copy() for disc→ISO raw sector dump
- IOStream trait deleted, all byte-level Read/Write removed
- ContentReader/OpenDisc/open_title/open_input/open_output deleted
- CountingStream wrapper for progress tracking

Error codes:
- All io::Error English strings replaced with Error enum variants
- From<Error> for io::Error conversion
- Unused variants removed, new stream/mux variants added

Deleted: mkvout.rs, pesout.rs, isowriter.rs, mkv-muxer-plan.md
Updated: all docs, README stream table, CHANGELOG

238 tests, 0 clippy warnings.

src/mux/network.rs

@@ -60,12 +60,7 @@ impl NetworkStream {
 
         // Read FMKV metadata header
         let disc_title = meta::read_header(&mut reader)?
-            .ok_or_else(|| {
-                io::Error::new(
-                    io::ErrorKind::InvalidData,
-                    "no FMKV metadata header from sender",
-                )
-            })?
+            .ok_or_else(|| -> io::Error { crate::error::Error::NoMetadata.into() })?
             .to_title();
 
         Ok(Self {
@@ -79,7 +74,7 @@ impl crate::pes::Stream for NetworkStream {
     fn read(&mut self) -> io::Result<Option<crate::pes::PesFrame>> {
         match &mut self.mode {
             Mode::Read { reader } => crate::pes::PesFrame::deserialize(reader),
-            _ => Err(io::Error::new(io::ErrorKind::Unsupported, "network opened for writing")),
+            _ => Err(crate::error::Error::StreamWriteOnly.into()),
         }
     }
     fn write(&mut self, frame: &crate::pes::PesFrame) -> io::Result<()> {
@@ -94,7 +89,7 @@ impl crate::pes::Stream for NetworkStream {
                 }
                 frame.serialize(writer)
             }
-            _ => Err(io::Error::new(io::ErrorKind::Unsupported, "network opened for reading")),
+            _ => Err(crate::error::Error::StreamReadOnly.into()),
         }
     }
     fn finish(&mut self) -> io::Result<()> {