Support pymatgen JSON format

[awvwgk]

• read pymatgen JSON
• write pymatgen JSON
• test all edge cases

[codecov]

Codecov Report

❌ Patch coverage is 84.45476% with 201 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.37%. Comparing base (89a04bd) to head (05d6ad0).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/mctc/io/write/pymatgen.f90	28.90%	4 Missing and 87 partials ⚠️
test/test_read_pymatgen.f90	94.41%	0 Missing and 57 partials ⚠️
src/mctc/io/read/pymatgen.F90	68.26%	2 Missing and 31 partials ⚠️
test/test_write_pymatgen.f90	55.26%	0 Missing and 17 partials ⚠️
src/mctc/io/filetype.f90	0.00%	0 Missing and 1 partial ⚠️
src/mctc/io/read.f90	0.00%	1 Missing ⚠️
src/mctc/io/write.f90	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #95      +/-   ##
==========================================
+ Coverage   70.98%   72.37%   +1.39%     
==========================================
  Files          80       84       +4     
  Lines       11281    12574    +1293     
  Branches     3455     3692     +237     
==========================================
+ Hits         8008     9101    +1093     
- Misses        759      767       +8     
- Partials     2514     2706     +192     

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