Add rerun --save: stream incoming log stream to an rrd file

[emilk]

By popular request!

This allows you to save incoming log messages directly to disk with rerun --save foo.rrd.

This can be useful when you have multiple processes logging to the same rerun server, and you want to save it all to an .rrd file.

Testing

In one terminal:

❯ RUST_LOG=debug cargo r -p rerun -- --save test.rrd
[2023-03-21T17:49:09Z INFO  re_sdk_comms::server] Hosting a SDK server over TCP at 0.0.0.0:9876. Connect with the Rerun logging SDK.
[2023-03-21T17:49:09Z WARN  rerun::run] Overwriting existing file at "test.rrd"
[2023-03-21T17:49:09Z INFO  rerun::run] Saving incoming log stream to "test.rrd". Abort with Ctrl-C.
[2023-03-21T17:49:16Z INFO  re_sdk_comms::server] New SDK client connected: 127.0.0.1:55903
[2023-03-21T17:49:17Z DEBUG re_sdk_comms::server] Client sent goodbye message.
^C[2023-03-21T17:49:23Z DEBUG rerun::run] Ctrl-C detected, shutting down.
[2023-03-21T17:49:23Z INFO  rerun::run] Log stream disconnected, stopping.
[2023-03-21T17:49:23Z INFO  rerun::run] File saved to "test.rrd"

In another terminal

cargo r -p objectron -- --connect

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct

[emilk]

Not sure what to label this… we may need a rerun CLI label