new collection based on easy_list

[rozyczko]

CollectionBase derived from EasyList

• Derives from EasyList rather than re-implementing MutableSequence from scratch.
• Removes all functionality now owned by EasyList (sequence operations, type protection, deduplication, serialization).
• Assumes legacy collection-specific concerns such as graph edges, interface propagation,
  and NotarizedDict have already been removed before this class is introduced.

Inheritance Hierarchy

NewBase
  └── EasyList[T]                   ← full MutableSequence, serialization, type protection
        └── CollectionBase[T]       ← adds aggregation methods only

content:

1. Parameter / Variable Aggregation

get_all_variables(self)
get_all_parameters(self)
get_parameters(self)
get_fittable_parameters(self)
get_free_parameters(self)
get_fit_parameters(self)

These mirror the methods on ModelBase, but aggregate across the list of items rather than
across the attribute names of a single object.

2. data Property

3. Legacy Serialization (_convert_to_dict)
   Support for the legacy encoder-based serialization path.
   Serializes all items in _data under the 'data' key, consistent with the old CollectionBase._convert_to_dict signature.

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