Move PymatgenTest.TEST_FILES_DIR attribute into module scope

[janosh]

e734bf3 fix IonEntry doc str + type hints
66d0043 move TEST_FILES_DIR attr from PymatgenTest into module scope
ca3c9e3 PymatgenTest.TEST_FILES_DIR -> TEST_FILES_DIR

[codecov-commenter]

Codecov Report

Patch coverage: 85.00% and no project coverage change.

Comparison is base (9455830) 74.57% compared to head (fbe07e3) 74.57%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3227   +/-   ##
=======================================
  Coverage   74.57%   74.57%           
=======================================
  Files         230      230           
  Lines       69493    69493           
  Branches    16166    16166           
=======================================
+ Hits        51823    51824    +1     
+ Misses      14596    14595    -1     
  Partials     3074     3074           

Files Changed	Coverage Δ
pymatgen/io/vasp/inputs.py	86.81% <50.00%> (ø)
pymatgen/analysis/pourbaix_diagram.py	89.07% <100.00%> (ø)
pymatgen/io/abinit/inputs.py	78.83% <100.00%> (ø)
pymatgen/util/testing.py	87.50% <100.00%> (ø)

... and 3 files with indirect coverage changes

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