Fix stream_block buffer cycling issue with FFPlay

PROBLEM:
When streaming Radio Paradise blocks via HTTP using FFPlay, the buffer
would cycle between 0KB and ~130KB approximately once per second, causing
audio dropouts and interruptions. VLC worked fine, but FFPlay was sensitive
to the burst transmission pattern.

ROOT CAUSE:
In StreamingFlacSink::broadcast_flac_stream(), the broadcaster was reading
8KB (8192 bytes) at a time from the FLAC encoder and sending the entire
chunk at once to all HTTP clients. This created a "burst" pattern:
- Read 8KB from encoder
- Send entire 8KB chunk to all clients
- Sleep if ahead of real-time pacing
- Repeat

FFPlay's buffer would fill rapidly with each 8KB burst, then drain completely
before the next burst arrived, causing the observed cycling behavior.

SOLUTION:
Reduced the HTTP broadcast buffer size from 8KB to 512 bytes in
StreamingFlacSink::broadcast_flac_stream(). This creates a much smoother,
more continuous data flow that FFPlay can handle without buffer cycling.

The 512-byte buffer size is:
- Small enough to prevent burst transmission
- Large enough to avoid excessive overhead
- Sufficient for smooth streaming with real-time pacing

CHANGES:
- Restore stream_block.rs example from git history
- Restore StreamingFlacSink and StreamingOggFlacSink from git history
- Add "streaming" feature to pmoaudio-ext
- Reduce broadcast buffer from 8192 to 512 bytes
- Update pmoparadise to use pmoaudio-ext streaming feature

TESTING:
Test with FFPlay to verify smooth buffering:
```bash
cargo run --example stream_block --features full -- 0
# In another terminal:
ffplay http://localhost:8080/test/stream
```

Watch the "aq=" value in FFPlay output. It should now remain stable
instead of cycling between 0KB and 130KB.

Cargo.lock

@@ -2867,6 +2867,7 @@ name = "pmoaudio-ext"
 version = "0.1.0"
 dependencies = [
  "async-trait",
+ "bytes",
  "pmoaudio",
  "pmoaudiocache",
  "pmocache",
@@ -2874,6 +2875,7 @@ dependencies = [
  "pmoflac",
  "pmometadata",
  "pmoplaylist",
+ "serde",
  "tokio",
  "tokio-util",
  "tracing",