Return errors on invalid entity paths

[emilk]

We currently have this in our code:

impl From<&str> for EntityPath {
    #[inline]
    fn from(path: &str) -> Self {
        path.parse().unwrap()
    }
}

impl From<String> for EntityPath {
    #[inline]
    fn from(path: String) -> Self {
        path.parse().unwrap()
    }
}

This means that passing an invalid entity path (e.g. ///åmål! ) to Rerun can crash the SDK, viewer, or both.

We should remove these and return errors on invalid paths instead.

[emilk]

Another solution to this is to allow anything as an entity path, and just doing our best to parse and interpret it, and perhaps log a warning if does not follow our preferred style.
For instance, /// ///foo/Hallå där.Text would be interpreted as " "/foo/"Hallå där.Text"