Added convenience method Dataset.add_private to add a private tag (#1… #3

Job	Run time
tests (macos, 3.10, true, false) / tests	2m 47s
tests (windows, 3.11, true, true) / tests	9m 41s
tests (ubuntu, pypy3.10, false, false) / tests	9m 8s
tests (ubuntu, 3.10, false, false) / tests	1m 33s
	23m 9s

Provide feedback