Subscriber/Queryable api alignment

[DenisBiryukov91]

remove z_undeclare_subscriber/publisher/queryable; make z_subscriber/publisher/queryable_drop automatically undeclare corresponding entities; add z_declare_background_subscriber/queryable functions, that do not return an entity, but rather register the corresponding callbacks until the session is closed/dropped; fix memory leaks in publisher due to non-cleared encoding and write_filter;

[github-actions[bot]]

PR missing one of the required labels: {'documentation', 'breaking-change', 'internal', 'new feature', 'dependencies', 'enhancement', 'bug'}