Composition raise ValueError if formula string is only numbers and spaces

[janosh]

Controlled by new strict: bool = True parameter to _parse_formula.

[CompRhys]

Doesn't catch the "NaN" -> float("NaN") edge case

>>> Composition(float("NaN"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pymatgen/pymatgen/core/composition.py", line 127, in __init__
    elem_map = dict(*args, **kwargs)  # type: ignore
TypeError: 'float' object is not iterable
>>> float("NaN")
nan

I was going to add another check:

from math import isnan
...
        if len(args) == 1 and isinstance(args[0], Composition):
            elem_map = args[0]
        elif len(args) == 1 and isinstance(args[0], str):
            elem_map = self._parse_formula(args[0])  # type: ignore
        elif len(args) == 1 and isnan(args[0]):
            raise ValueError("float('NaN') is not a valid Composition, did you mean str('NaN')?")
        else:
            elem_map = dict(*args, **kwargs)  # type: ignore