Request to add double precision suport to fixed_radius_search

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](https://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](https://www.open3d.org/docs/release/) and the [latest documentation](https://www.open3d.org/docs/latest/) (for `main` branch).

### Proposed new feature or change

i found when build torch ops and use cuda module, the `fixed_radius_search`function don't support double type,and unit test said that the GPU only supports single precision float.can i impl double precision support for this function?

### References

_No response_

### Additional information

_No response_