Delay list -> dict conversation to end

[vidartf]

This should prevent dicts in webapp data from being clobbered by converted lists from the settings_dir.

Fixes #191 .

• TODO: Add tests.

[codecov-commenter]

Codecov Report

Merging #192 (cdc21cd) into main (04fcf0e) will increase coverage by 0.45%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #192      +/-   ##
==========================================
+ Coverage   77.48%   77.93%   +0.45%     
==========================================
  Files          28       28              
  Lines        2105     2121      +16     
==========================================
+ Hits         1631     1653      +22     
+ Misses        474      468       -6     

Impacted Files	Coverage Δ
jupyterlab_server/config.py	66.27% <100.00%> (+2.90%)	⬆️
jupyterlab_server/handlers.py	88.09% <100.00%> (+0.29%)	⬆️
jupyterlab_server/pytest_plugin.py	93.65% <100.00%> (+0.31%)	⬆️
jupyterlab_server/tests/test_labapp.py	100.00% <100.00%> (ø)

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[vidartf]

@minrk This setting will interact with the hook introduced in #220 by expecting certain keys to now map to dicts instead of lists. Have you been using any such keys in hub yet? (see the added test for details)

[minrk]

I haven't yet, but it shouldn't be a problem for us. Thanks for the heads up.

[jtpio]

This setting will interact with the hook introduced in #220 by expecting certain keys to now map to dicts instead of lists.

Should this be considered a breaking change?

After investigating the JupyterLab CI failure in jupyterlab/jupyterlab#11744, it looks like consumers retrieving the page config with get_page_config now get dicts instead of lists. This is causing issues with disabled extensions in JupyterLab with jupyterlab_server>=2.10 when using the CLI (jupyterlab/jupyterlab#11744 (comment)).

This could be fixed in lab, but would need to be able to handle both dicts and lists to allow for various combinations of jupyterlab and jupyterlab_server (< 2.10 or >=2.10).