Add LexicalExpander: weighted synonym and hypernym expansion over the lexical knowledge base

Expands a term into the synonyms sharing its synsets, the lemmas of its
hypernym ancestors up to a configured depth (following both the direct and
the instance relation), and optionally its direct hyponyms. Each expansion
carries a deterministic heuristic weight: sense rank and every relation
step multiply configurable decays, so consumers can discount looser
expansions instead of treating them as the original term. Results exclude
the input, deduplicate case-insensitively keeping the highest weight, and
order stably by weight, kind, and term.

Inflected input works through an optional Lemmatizer invoked with the
WordNetPos name as the tag, which the Morphy lemmatizer understands: dogs
expands through dog, mice through the exception list to mouse. Hypernym
walks are visited-checked so malformed cyclic data terminates.

Tests cover the graph behavior on a hand-built lexicon (sense ranking,
decay arithmetic, dedup, cycle termination, validation) and run the whole
stack over the miniature WN-LMF and WNDB fixtures, asserting both readers
produce identical expansions.

Author: krickert