Increased performances of lookup3d nearest search.

src/mol-math/geometry/_spec/lookup3d.spec.ts

src/mol-math/geometry/lookup3d/common.ts

src/mol-math/geometry/lookup3d/grid.ts

src/mol-model/structure/structure/util/lookup3d.ts

src/mol-util/_spec/fibonacci-heap.spec.ts

src/mol-util/fibonacci-heap.ts