Add .tools.check()

[khaeru]

This PR adds a new function message_ix.tools.check().

This function does pre-solve checks on MESSAGE-scheme scenarios: it examines the contents of a Scenario object and returns failure or warning if the contents of the Scenario are not compatible with the MESSAGE GAMS implementation and will certainly or likely cause an error if Scenario.solve() is called.

Details:

• This parallels some existing "sanity checks" already implemented in the GAMS code itself, e.g.

  message_ix/message_ix/model/MESSAGE/data_load.gms

  Lines 175 to 177 in 900a9f8

  	*----------------------------------------------------------------------------------------------------------------------*
  	* sanity checks on the data set *
  	*----------------------------------------------------------------------------------------------------------------------*

  
  Since GAMS is not a general-purpose programming language, checks in Python with more sophisticated checks and informative error messages can be easier to write and maintain.
• The check() method returns a list of Result objects. This is a simple class that includes a description of the check, the outcome (pass, fail, warning) and optional informative messages that can explain the offending contents of the scenario.
• The first Result is an "overall" result, only passing if all the other checks pass.
• The list of checks is extensible.
• The implementation uses message_ix.reporting (ultimately genno) internally.

How to review

• Read the diff and note that the CI checks all pass.
• View the added documentation and ensure the checks are fully described.

PR checklist

• Extend checks
  • Non-integer technical_lifetime → error in scaling_investment_costs.gms #503
• Continuous integration checks all ✅
• Add or expand tests; coverage checks both ✅
• Add, expand, or update documentation.
• Update release notes.

[codecov]

Codecov Report

Merging #506 (c1be92a) into main (900a9f8) will increase coverage by 0.1%.
The diff coverage is 96.6%.

❗ Current head c1be92a differs from pull request most recent head 4dae5fb. Consider uploading reports for the commit 4dae5fb to get more accurate results

@@           Coverage Diff           @@
##            main    #506     +/-   ##
=======================================
+ Coverage   93.4%   93.5%   +0.1%     
=======================================
  Files         38      41      +3     
  Lines       2853    2967    +114     
=======================================
+ Hits        2666    2776    +110     
- Misses       187     191      +4     

Impacted Files	Coverage Δ
message_ix/tests/tools/test_check.py	90.0% <90.0%> (ø)
message_ix/tools/_check.py	98.7% <98.7%> (ø)
message_ix/reporting/__init__.py	100.0% <100.0%> (ø)
message_ix/tests/test_tutorials.py	100.0% <100.0%> (ø)
message_ix/tools/__init__.py	100.0% <100.0%> (ø)