pypgstac is not compatible with Python 3.7

[drnextgis]

It is declared here that pypgstac supports Python >= 3.7. But current code is not compatible with Python 3.7 due to the way lru_cache is being used here:

$ python3.7
Python 3.7.5 (default, Dec  9 2021, 17:04:37) 
[GCC 8.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from functools import lru_cache
>>> @lru_cache
... def f():
...     pass
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.7/functools.py", line 490, in lru_cache
    raise TypeError('Expected maxsize to be an integer or None')
TypeError: Expected maxsize to be an integer or None