configure method
Declare which metadata fields this store should make filterable.
Called once at registration, before initialize — the schema is
threaded from FlutterGemma.initialize(filterSchema:) through the service
registry into the store's constructor wiring, so the store can promote the
declared fields to typed storage columns (vec0) or top-level payload keys
(qdrant) the first time it creates its table / writes a document.
Default is a no-op: a store that does not override this keeps ignoring
filters, and the never-throws contract on searchSimilar still holds — an
empty or undeclared-key Filter returns the same hits as filter: null,
it never throws.
Implementation
@override
void configure(FilterSchema schema) {}