Specify data type for the entropy array

[visika]

This solves a issue I encountered, when reading thermal properties from a yaml file; the numbers in the array of the entropy are read as strings for some reason, and this collides with numpy at some point. I would get the following error otherwise:

Traceback (most recent call last):
  File "/home/---/QHA/phonopy-qha.py", line 321, in <module>
    main(get_options())
  File "/home/---/QHA/phonopy-qha.py", line 253, in main
    phonopy_qha = PhonopyQHA(
                  ^^^^^^^^^^^
  File "/home/---/.cache/pypoetry/virtualenvs/---W3b-Z9Lh-py3.11/lib/python3.11/site-packages/phonopy/api_qha.py", line 128, in __init__
    self._qha.run(verbose=verbose)
  File "/home/---/.cache/pypoetry/virtualenvs/----W3b-Z9Lh-py3.11/lib/python3.11/site-packages/phonopy/qha/core.py", line 408, in run
    self._set_heat_capacity_P_polyfit()
  File "/home/---/.cache/pypoetry/virtualenvs/----W3b-Z9Lh-py3.11/lib/python3.11/site-packages/phonopy/qha/core.py", line 1120, in _set_heat_capacity_P_polyfit
    parameters = np.polyfit(self._volumes, self._entropy[j], 4)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/---/.cache/pypoetry/virtualenvs/----W3b-Z9Lh-py3.11/lib/python3.11/site-packages/numpy/lib/polynomial.py", line 631, in polyfit
    y = NX.asarray(y) + 0.0
        ~~~~~~~~~~~~~~^~~~~
numpy.core._exceptions._UFuncNoLoopError: ufunc 'add' did not contain a loop with signature matching types (dtype('<U32'), dtype('float64')) -> None

[atztogo]

I don't understand why. But I have no reason not to accept your change.

Could you replace "float64" by "double"? It is just because it is made so for the other part of phonopy.

[visika]

I think I encountered a edge case. As I'm not an expert user of phonopy, I might be misunderstanding its use. I will try to explain what scenario I'm facing in a separate issue to keep the pull requests list clean.