Add --stdout/-o to our CLI helper library (#4544)

You can now pipe all Python & Rust examples into a Rerun Viewer.


![image](https://github.com/rerun-io/rerun/assets/2910679/ff65e6f9-a5e6-497f-a108-577fcd0c6e57)


Checks:
- [x] python examples/python/minimal_options/main.py -o | rerun -
- [x] cargo r -p minimal_options -- -o | rerun -

crates/rerun/src/clap.rs

@@ -12,6 +12,8 @@ enum RerunBehavior {
 
     Save(PathBuf),
 
+    Stdout,
+
     #[cfg(feature = "web_viewer")]
     Serve,
 
@@ -47,6 +49,10 @@ pub struct RerunArgs {
     #[clap(long)]
     save: Option<PathBuf>,
 
+    /// Log data to standard output, to be piped into a Rerun Viewer.
+    #[clap(long, short = 'o')]
+    stdout: bool,
+
     /// Connects and sends the logged data to a remote Rerun viewer.
     ///
     /// Optionally takes an `ip:port`.
@@ -89,6 +95,11 @@ impl RerunArgs {
     #[track_caller] // track_caller so that we can see if we are being called from an official example.
     pub fn init(&self, application_id: &str) -> anyhow::Result<(RecordingStream, ServeGuard)> {
         match self.to_behavior()? {
+            RerunBehavior::Stdout => Ok((
+                RecordingStreamBuilder::new(application_id).stdout()?,
+                Default::default(),
+            )),
+
             RerunBehavior::Connect(addr) => Ok((
                 RecordingStreamBuilder::new(application_id)
                     .connect_opts(addr, crate::default_flush_timeout())?,
@@ -144,6 +155,10 @@ impl RerunArgs {
 
     #[allow(clippy::unnecessary_wraps)] // False positive on some feature flags
     fn to_behavior(&self) -> anyhow::Result<RerunBehavior> {
+        if self.stdout {
+            return Ok(RerunBehavior::Stdout);
+        }
+
         if let Some(path) = self.save.as_ref() {
             return Ok(RerunBehavior::Save(path.clone()));
         }

rerun_py/rerun_sdk/rerun/script_helpers.py

@@ -51,6 +51,13 @@ def script_add_args(parser: ArgumentParser) -> None:
     )
     parser.add_argument("--addr", type=str, default=None, help="Connect to this ip:port")
     parser.add_argument("--save", type=str, default=None, help="Save data to a .rrd file at this path")
+    parser.add_argument(
+        "-o",
+        "--stdout",
+        dest="stdout",
+        action="store_true",
+        help="Log data to standard output, to be piped into a Rerun Viewer",
+    )
 
 
 def script_setup(
@@ -77,7 +84,9 @@ def script_setup(
     rec: RecordingStream = rr.get_global_data_recording()  # type: ignore[assignment]
 
     # NOTE: mypy thinks these methods don't exist because they're monkey-patched.
-    if args.serve:
+    if args.stdout:
+        rec.stdout()  # type: ignore[attr-defined]
+    elif args.serve:
         rec.serve()  # type: ignore[attr-defined]
     elif args.connect:
         # Send logging data to separate `rerun` process.