remove seek support for (lewton) vorbis

seek is broken, RustAudio/lewton#73.
We could work around it by:
 - using unsafe to create an instance of Self
 - use mem::swap to turn the &mut self into a mut self
 - take out the underlying Read+Seek
 - make a new self and seek

If this issue is fixed use the implementation in
commit: 3bafe32

src/decoder/vorbis.rs

@@ -76,39 +76,20 @@ where
         None
     }
 
+    /// seek is broken, https://github.com/RustAudio/lewton/issues/73. 
+    // We could work around it by:
+    //  - using unsafe to create an instance of Self
+    //  - use mem::swap to turn the &mut self into a mut self
+    //  - take out the underlying Read+Seek
+    //  - make a new self and seek
+    //
+    // If this issue is fixed use the implementation in
+    // commit: 3bafe32388b4eb7a48c6701e6c65044dc8c555e6
     #[inline]
-    fn try_seek(&mut self, pos: Duration) -> Result<(), SeekError> {
-        // note sample rate in vorbis encoding is constant
-        let samples = pos.as_secs_f32() * self.sample_rate() as f32;
-        self.stream_reader.seek_absgp_pg(samples as u64)?;
-
-        // first few frames (packets) sometimes fail to decode, if
-        // that happens just retry a few times.
-        let mut last_err = None;
-        for _ in 0..10 {
-            // 10 seemed to work best in testing
-            let res = self.stream_reader.read_dec_packet_itl();
-            match res {
-                Ok(data) => {
-                    match data {
-                        Some(d) => self.current_data = d,
-                        None => self.current_data = Vec::new(),
-                    }
-                    // make sure the next seek returns the
-                    // sample for the correct speaker
-                    let to_skip = self.next % self.channels() as usize;
-                    for _ in 0..to_skip {
-                        self.next();
-                    }
-                    return Ok(());
-                }
-                Err(e) => last_err = Some(e),
-            }
-        }
-
-        Err(SeekError::LewtonDecoder(
-            last_err.expect("is set if we get out of the for loop"),
-        ))
+    fn try_seek(&mut self, _: Duration) -> Result<(), SeekError> {
+        Err(SeekError::NotSupported {
+            underlying_source: std::any::type_name::<Self>(),
+        })
     }
 }
 

tests/seek.rs

@@ -204,15 +204,15 @@ fn seek_does_not_break_channel_order() {
             is_silent(&samples, source.channels(), channel0),
             "channel0 should be silent, 
     channel0 starts at idx: {channel0}
-    seek offset: {offset:?}
+    seek: {beep_start:?} + {offset:?}
     samples: {samples:?}"
         );
         let channel1 = (1 + channel_offset) % 2;
         assert!(
             !is_silent(&samples, source.channels(), channel1),
             "channel1 should not be silent, 
     channel1; starts at idx: {channel1}
-    seek offset: {offset:?}
+    seek: {beep_start:?} + {offset:?}
     samples: {samples:?}"
         );
     }