mux: mpg:// program-stream output and source

A container-neutral fit plan, then mpg:// as an H.222.0 program-stream
sink on the PES IR and as a source through the DVD sector pipeline. PES
and AU placement, start-up hold caps and 20/24-bit LPCM timing follow
the spec; a clear MPEG-1/2 PS is never read as scrambled and CSS is
judged per pack. E9074 for an output with no video track.

tests/crypto_tests.rs

@@ -24,6 +24,8 @@ fn css_descramble_sector_roundtrip_via_public_api() {
     // requires the pack start code as well as the flag bits — byte 0x14 means
     // something else entirely in an IFO or UDF sector.
     sector[0x00..0x04].copy_from_slice(&[0x00, 0x00, 0x01, 0xBA]);
+    sector[4] = 0x44; // '01': a 13818-1 pack
+    sector[0x0D] = 0xF8; // pack_stuffing_length 0
     sector[0x14] = 0x30;
     sector[0x54..0x59].copy_from_slice(&[0xDE, 0xAD, 0xBE, 0xEF, 0x42]);
     let original = sector.clone();