Data structure traversal support

NLP data structures themselves are often interesting. It is often required to traverse a tree or follow a path in a graph in NLP. For example, one can follow the dependency tree to find the headword, or follow a network path (following specific relation links). This can be supported by Forte in a natural way, and we can at the same time attach relevant features to the path (e.g. embeddings along the path, or relation labels along the path).

The issue names no files, tests, or entry points. Start by clarifying the required tree and graph traversal behavior in Forte, including how paths and attached features should be represented; done means the supported traversal and feature-attachment scope is defined and validated.

Written by the indexing model from the issue text.