Introduce Extension Components

[jleibs]

Add your own meta-data to anything you log.

Standalone API:

    rr.log_extension_components("extension_components/point", {"confidence": 0.9})

Or optional arg for all of the existing APIs:

    rr.log_points(
        "user_components/points",
        np.array([[32, 32], [32, 96], [96, 32], [96, 96]]),
        ext={"corner": ["upper left", "lower left", "upper right", "lower right"]},
    )

Behind the scenes we track both the inferred numpy type and arrow type and thereafter use those to attempt to do type-conversions. If the conversion fails we just warn and drop the component. This gives us fairly reasonable and forgiving behavior without violating the needs of the data-store to have a single type-per-component.

The data is visible through both hover and selection:

Resolves: #401

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I've added a line to CHANGELOG.md (if this is a big enough change to warrant it)

[emilk]

This seems weird to me. A user can set a single color as an argument, and then it will be a splat, and should go into splats. Same with label etc

[jleibs]

This didn't change the behavior that was there -- just highlighted the issue. The core of what you're seeing is the fact that the arrow3d API doesn't expose batches at all. There is no "log_arrows" at the moment. I agree we should do a pass to make this consistent across the board, but this isn't the PR to do it.

[nikolausWest]

I'm so excited for this feature! I've been playing around with it a bit an was very pleasantly surprised that it already works so well. Because it's so useful I directly found I wanted #1024 when using it.

One thing I'd really like to change: the names "user_components" in the SDK and "user" in the Viewer.

I don't like the word "user", as it conveys that this is just a small corner on the side for the user's own stuff. I think we should use something like extend, extension, or extra. I also think the parameter to the logging function should be super short, perhaps even ext.

[jondo2010]

Seems like a good stop-gap until we have the runtime component registry

[nikolausWest]

Nice!