fix(audio): three 100% CPU busy loops on the _pa path (#16229)

The Linux audio service in `--server` ignored the `Err` from `next_raw()`, so
once the cm-side `_pa` peer closed, every iteration re-polled a dead socket:
tokio-util's paused `Framed` issues one 0-byte read per poll and returns ready
at once, never `Pending`. The thread never parked and burned a full core for
the life of the process. Propagate instead, so `ServiceTmpl::run`'s existing
backoff ends the inner loop and reconnects.

Two sibling loops on the same audio path have the same shape:

- `ipc::start_pa` (runs in `--cm`) ignored the `Err` from
  `psimple::Simple::read`, so a dead pulse handle spins there instead.
- `start_voice_call`'s forwarding thread polls two channels with `try_recv`
  and has no blocking primitive at all: measured 99.8% of a core for the whole
  call, against 1.0% with a 1 ms pause (audio packets arrive every 10 ms).

fix https://github.com/rustdesk/rustdesk/issues/16226

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/client/io_loop.rs

@@ -598,6 +598,9 @@ impl<T: InvokeUiSession> Remote<T> {
                             } else {
                                 log::debug!("Failed to record local audio channel: {}", err);
                             }
+                            // Both arms fall through with nothing else in this loop blocking, so
+                            // without a pause the thread spun a core for the whole voice call.
+                            std::thread::sleep(std::time::Duration::from_millis(1));
                         }
                     }
                 }