more refactoring

src/mol-base/collections/_spec/int-tuple.spec.ts

src/mol-base/collections/_spec/interval.spec.ts

src/mol-base/collections/_spec/ordered-set.spec.ts

src/mol-base/collections/_spec/segmentation.spec.ts

src/mol-base/collections/_spec/sorted-array.spec.ts

src/mol-base/collections/integer/impl/interval.ts

src/mol-base/collections/integer/impl/ordered-set.ts

src/mol-base/collections/integer/impl/segmentation.ts

src/mol-base/collections/integer/impl/sorted-array.ts

src/mol-base/collections/integer/interval.ts

src/mol-base/collections/integer/ordered-set.ts

src/mol-base/collections/integer/segmentation.ts

src/mol-base/collections/integer/sorted-array.ts

src/mol-base/collections/integer/tuple.ts

src/mol-data/_spec/atom-set.spec.ts

src/mol-data/atom-set.ts

src/mol-data/atom-set/base.ts

src/mol-data/atom-set/builder.ts

src/mol-data/model.ts

src/perf-tests/sets.ts