Fix caching bugs in rails reloading

[yourpalal]

Add slightly more aggressive clearing of caches during rails reloads.

Fixes query results being wrapped in stale classes after a reload.

This pull introduces/changes:

• adds ActiveGraph::Node::Labels::Reloading.prepare_for_unload! method
• call to prepare_for_unload! in an ActiveSupport::Reloader.before_class_unload callback
• document use of deprecated/removed method
• replace MODELS_FOR_LABELS_CACHE.clear with ActiveGraph::Node::Labels.clear_wrapped_models, which clears that cache as well as another one!

[codeclimate[bot]]

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[yourpalal]

@klobuczek the build errored here due to a failing wget command

The command "wget https://bootstrap.pypa.io/get-pip.py && python3 get-pip.py --user" failed and exited with 1 during .

I'm not sure if this is just a transient issue, but could the build be re-run?