Only write groups in Turbomole output if necessary

[awvwgk]

For compatibility with less flexible Turbomole readers.

• write in decimal format by default, switch to scientific notation for large numbers
• don't write the $eht group in case the system is uncharged or has no unpaired electrons
• only write $periodic group for if there is at least one periodic dimension

[codecov[bot]]

Codecov Report

Merging #41 (209a885) into main (3d0e921) will decrease coverage by 0.07%. The diff coverage is 11.11%.

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
- Coverage   69.88%   69.80%   -0.08%     
==========================================
  Files          60       60              
  Lines        7610     7615       +5     
  Branches     2227     2232       +5     
==========================================
- Hits         5318     5316       -2     
- Misses        735      738       +3     
- Partials     1557     1561       +4     

Impacted Files	Coverage Δ
src/mctc/io/write/turbomole.f90	47.36% <11.11%> (-31.21%)	:arrow_down:

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