General improvements and bugfixes

[guillaume-chevalier]

General improvements and bugfixes:

• Update FlattenForEach that wasn't up to date
• Use _ids, data_inputs, and expected_outputs more often in DataContainer instead of shorthand ids, di, and eo, which were auto-filling values too often when looping over things in flow classes and output handlers
• Changed InputAndOutputTransformerMixin to IdsAndInputAndOutputTransformerMixin and derived classes to also process IDs more often in triplets rather than duo tuples of di and eo.
• Fixed bugs in DataContainer
• Easy to read string representation of the DataContainer (DACT) is now possible for easier print debugging at a glimpse
• Repair some skipped tests
• Cleaned some docstrings
• Add str and repr functionalities to context to show its services and parents in detail upon printing.
• _TruncableMixin that is common to _TruncableSteps and _TruncableService
• Introducing _TruncableServiceWithBodyMixin for .body and .joiner that is easier. Also fix FlattenForEach.
• Added different copy constructors to services depending on the AutoML train/val phase

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