Address tests that are flaky on GHA

[khaeru]

Some of the tutorial tests are "flaky": they occasionally fail on the GitHub Actions runners, e.g. here. This necessitates daily work to restart the CI runs.

Per the Pytest docs on flaky tests, this PR:

• Adds pytest-rerunfailures to the tests dependencies.
• Applies the "flaky" marker to these tutorial tests.

Also:

• Advertise Python 3.11 support in classifiers, and test against Python 3.11 on CI (parallel to Support Python 3.11 ixmp#481).
• Update deprecated usage in the test suite: mainly of float(…) to get a single value from a pandas.DataFrame; using DataFrame.at[…] or .item() instead.

How to review

Confirm at least one instance where a test initially fails, and the usage of the plugin succeeds in allowing the test to pass on re-run.

This should appear somewhat like this in the log output:

test_all.py::test_example RERUN   [100%]
test_all.py::test_example RERUN   [100%]
test_all.py::test_example PASSED  [100%]

====== 1 passed, 2 rerun in 0.01s ======

→ here, at L314, re-run at L318, and summarized at L17008.

PR checklist

• Continuous integration checks all ✅
• Add or expand tests; coverage checks both ✅
• Add, expand, or update documentation. N/A, testing only
• Update release notes.

[codecov]

Codecov Report

Merging #712 (9ef7a04) into main (6bfc29e) will decrease coverage by 0.1%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main    #712     +/-   ##
=======================================
- Coverage   94.4%   94.4%   -0.1%     
=======================================
  Files         43      43             
  Lines       3449    3448      -1     
=======================================
- Hits        3258    3257      -1     
  Misses       191     191             

Impacted Files	Coverage Δ
...age_ix/tests/test_feature_bound_activity_shares.py	100.0% <ø> (ø)
message_ix/tests/test_core.py	100.0% <100.0%> (ø)
message_ix/tests/test_feature_bound_emission.py	100.0% <100.0%> (ø)
message_ix/tests/test_feature_capacity_factor.py	100.0% <100.0%> (ø)
message_ix/tests/test_feature_duration_time.py	100.0% <100.0%> (ø)
message_ix/tests/test_feature_storage.py	100.0% <100.0%> (ø)
message_ix/tests/test_feature_temporal_level.py	100.0% <100.0%> (ø)
message_ix/tests/test_soft_constraints.py	100.0% <100.0%> (ø)
message_ix/tests/test_tutorials.py	100.0% <100.0%> (ø)
message_ix/tests/tools/test_add_year.py	95.6% <100.0%> (-0.2%)	⬇️

[khaeru]

We still see the following for macOS; all Python versions; for the R_austria tutorials:

Error in eval(expr, envir, enclos): java.lang.java.lang.UnsatisfiedLinkError: java.lang.UnsatisfiedLinkError: /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/ixmp/backend/jdbc/libgmdjni64.dylib: dlopen(/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/ixmp/backend/jdbc/libgmdjni64.dylib, 0x0001): Library not loaded: '@rpath/libgcc_s.1.dylib'
<... omitted ...>n.framework/Versions/3.11/lib/python3.11/site-packages/ixmp/backend/jdbc/./libgcc_s.1.dylib' (no such file), '/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/ixmp/backend/jdbc/./libgcc_s.1.dylib' (no such file), '/Users/runner/hostedtoolcache/Java_Temurin-Hotspot_jdk/8.0.372-7/x64/Contents/Home/jre/lib/server/./libgcc_s.1.dylib' (no such file), '/Users/runner/hostedtoolcache/Java_Temurin-Hotspot_jdk/8.0.372-7/x64/Contents/Home/jre/lib/server/../libgcc_s.1.dylib' (no such file), '/Library/Frameworks/R.framework

[glatterf42]

We still see the following for macOS; all Python versions; for the R_austria tutorials:

Error in eval(expr, envir, enclos): java.lang.java.lang.UnsatisfiedLinkError: java.lang.UnsatisfiedLinkError: /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/ixmp/backend/jdbc/libgmdjni64.dylib: dlopen(/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/ixmp/backend/jdbc/libgmdjni64.dylib, 0x0001): Library not loaded: '@rpath/libgcc_s.1.dylib'
<... omitted ...>n.framework/Versions/3.11/lib/python3.11/site-packages/ixmp/backend/jdbc/./libgcc_s.1.dylib' (no such file), '/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/ixmp/backend/jdbc/./libgcc_s.1.dylib' (no such file), '/Users/runner/hostedtoolcache/Java_Temurin-Hotspot_jdk/8.0.372-7/x64/Contents/Home/jre/lib/server/./libgcc_s.1.dylib' (no such file), '/Users/runner/hostedtoolcache/Java_Temurin-Hotspot_jdk/8.0.372-7/x64/Contents/Home/jre/lib/server/../libgcc_s.1.dylib' (no such file), '/Library/Frameworks/R.framework

See iiasa/ixmp#479 for a related issue without solution as of now.