Add StdioStream, IsoStream; enforce scheme:// URL format

- StdioStream: stdin/stdout pipe, format-agnostic
- IsoStream: read BD-TS from Blu-ray ISO images
- URL resolver: bare paths rejected, all URLs require scheme:// prefix
- Validation: empty paths, missing ports, read-only/write-only errors
- Tests: 22 passing (URL parsing, validation, metadata roundtrip)
- Docs: full stream table with 7 stream types

src/lib.rs

@@ -101,5 +101,7 @@ pub use mux::M2tsStream;
 pub use mux::NetworkStream;
 pub use mux::DiscStream;
 pub use mux::NullStream;
+pub use mux::StdioStream;
+pub use mux::IsoStream;
 pub use mux::DiscOptions;
 pub use mux::{open_input, open_output, parse_url, InputOptions};