Add hdf5 capabilities

[v1kko]

No description provided.

[stefsmeets]

I'm working on code to write back to hdf5 atm, could we link this to imas2xarray?

See: duqtools/imas2xarray#12

[v1kko]

That would solve the problem of IMAS just segfaulting when trying to open a HDF5 entry:

imas.DBEntry(imasdef.HDF5_BACKEND, self.db, self.shot, self.run, self.user) < this segfaults

So I am in favor of doing this via imas2xarray instead

[stefsmeets]

The plan:

• ImasHandle -> MDSPlusHandle (keep access through access layer), becomes legacy
• New HD5Handle, goes to imas2xarray for loading the data
• New way of operating on xarray (necessary to refactor on _apply_model)
• ImasPath (user,machine,shot,run), direct path (pathlib.Path)

[stefsmeets]

@v1kko Do you want to have a check before we merge this?

[stefsmeets]

I'm closing this in favour of #706