swarm/storage/localstore: new localstore package (#19015)

swarm/storage/localstore/doc.go

swarm/storage/localstore/gc.go

swarm/storage/localstore/gc_test.go

swarm/storage/localstore/index_test.go

swarm/storage/localstore/localstore.go

swarm/storage/localstore/localstore_test.go

swarm/storage/localstore/mode_get.go

swarm/storage/localstore/mode_get_test.go

swarm/storage/localstore/mode_put.go

swarm/storage/localstore/mode_put_test.go

swarm/storage/localstore/mode_set.go

swarm/storage/localstore/mode_set_test.go

swarm/storage/localstore/retrieval_index_test.go

swarm/storage/localstore/subscription_pull.go

swarm/storage/localstore/subscription_pull_test.go

swarm/storage/localstore/subscription_push.go

swarm/storage/localstore/subscription_push_test.go