Add ability to view constraint coords in LP files

[brynpickering]

I realised that although I added the ability for variables and expressions to be verbose, I missed out constraints. They are useful if verbose in the LP files.

Reviewer checklist:

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

[codecov[bot]]

Codecov Report

Merging #493 (fa6e264) into main (cbed4c8) will decrease coverage by 2.78%. Report is 5 commits behind head on main. The diff coverage is 96.10%.

@@            Coverage Diff             @@
##             main     #493      +/-   ##
==========================================
- Coverage   94.98%   92.21%   -2.78%     
==========================================
  Files          31       32       +1     
  Lines        3890     4021     +131     
  Branches        0      961     +961     
==========================================
+ Hits         3695     3708      +13     
- Misses        195      196       +1     
- Partials        0      117     +117     

Files	Coverage Δ
src/calliope/__init__.py	100.00% <ø> (ø)
src/calliope/_version.py	100.00% <ø> (ø)
src/calliope/backend/helper_functions.py	99.35% <ø> (ø)
src/calliope/backend/where_parser.py	98.55% <100.00%> (ø)
src/calliope/cli.py	81.67% <100.00%> (ø)
src/calliope/core/__init__.py	100.00% <ø> (ø)
src/calliope/core/attrdict.py	99.50% <ø> (ø)
src/calliope/core/io.py	91.75% <100.00%> (ø)
src/calliope/core/model.py	93.23% <100.00%> (ø)
src/calliope/core/util/generate_runs.py	87.09% <ø> (ø)
... and 22 more