impl Copy for Arrow3D. (#2239)

### What

`Arrow3D` is a simple pair of vectors, so it should be `Copy` like
vectors are. This will ease working with, for example, batches of arrows
stored in arrays.

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [ ] ~~I've included a screenshot or gif (if applicable)~~

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crates/re_log_types/src/component_types/arrow.rs

@@ -30,7 +30,7 @@ use crate::Component;
 ///     ])
 /// );
 /// ```
-#[derive(Clone, Debug, ArrowField, ArrowSerialize, ArrowDeserialize, PartialEq)]
+#[derive(Copy, Clone, Debug, ArrowField, ArrowSerialize, ArrowDeserialize, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub struct Arrow3D {
     pub origin: Vec3D,