Fix linter issues

[awvwgk]

Closes #203
Closes #204
Closes #205
Closes #206
Closes #207
Closes #208
Closes #209
Closes #210

[codecov]

Codecov Report

❌ Patch coverage is 20.68966% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.13%. Comparing base (2b16838) to head (d4730fb).

Files with missing lines	Patch %	Lines
src/dftd3/output.f90	20.00%	8 Missing and 8 partials ⚠️
src/dftd3/gcp.f90	0.00%	0 Missing and 4 partials ⚠️
app/argument.f90	0.00%	1 Missing ⚠️
app/toml.f90	0.00%	0 Missing and 1 partial ⚠️
src/dftd3/gcp/param.f90	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #213      +/-   ##
==========================================
+ Coverage   64.55%   65.13%   +0.57%     
==========================================
  Files          36       36              
  Lines        5073     5099      +26     
  Branches     1775     1805      +30     
==========================================
+ Hits         3275     3321      +46     
+ Misses        810      740      -70     
- Partials      988     1038      +50     

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