Modify RISP_data() to return all bins in the file

I noticed that there is a difference across pulse types here. For FP, `data` contains all bins (hence we need to use `[bin_index]`. This is not the case for RISP.

We can maybe simplify this function greatly if we modify the `RISP_data()` method to return the whole dataframe (for all bins in the file) and not slice it. At least this would make this more understandable

_Originally posted by @RemDelaporteMathurin in https://github.com/kaelyndunnell/hisp/pull/64#discussion_r1874004321_