Direct user-to-user transfer edges among a wallet set

Returns the set of direct transfer edges (user-to-user, scoped to a mint) where both endpoints are in the supplied wallet list. Edges are canonical (a < b lex), undirected, and aggregated — repeated transfers between the same pair collapse to one row with a transfers count.

Used by the bubblemap to draw lines between holders that have directly interacted; useful generally for “did wallet A ever send tokens to wallet B?” style queries.