Model class cleanup: fix `info` & remove empty method; add docstrings.

[brynpickering]

Just added some missing docstrings and fixed a function giving general info on the model.

Reviewer checklist:

• [ ] Test(s) added to cover contribution
• [ ] Documentation updated
• [ ] Changelog updated
• [ ] Coverage maintained or improved

[codecov[bot]]

Codecov Report

Merging #468 (9913018) into main (66e94fb) will decrease coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #468      +/-   ##
==========================================
- Coverage   94.88%   94.88%   -0.01%     
==========================================
  Files          31       31              
  Lines        3814     3813       -1     
==========================================
- Hits         3619     3618       -1     
  Misses        195      195              

Impacted Files	Coverage Δ
calliope/core/model.py	95.77% <100.00%> (-0.02%)	:arrow_down: