dynamic_sizing fields

[jviquerat]

Hi,

First, thanks for this repo.
I may be wrong, but for datasets flag_dynamic_sizing and sphere_dynamic_sizing (download through the .sh script), the dynamic_sizing field in the .json file has strange attributes:

"sizing_field": {
      "type": "dynamic_varlen",
      "shape": [
        -1,
        4
      ],
      "dtype": "<dtype: 'float32'>"
    }

This raises a first attribute error due to the malformed dtype, then a second reshape error.
Modifying to:

"sizing_field": {
      "type": "dynamic_varlen",
      "shape": [
        -1,
        3
      ],
      "dtype": "float32"
    }

seems to solve the problem.