fix: move read invalid check to diffsuppressfunc

[jbe-dw]

Proposition to #79

The test is removed from the read function. A diffsuppressfunc is added instead:

• The NS in the state reflects the ones in the server
• When "namervers" is unset or set to an empty list, the change is ignored.

The tests are passing now.

[jbe-dw]

After more tests, the DiffSupressFunc is applied on each item of the list. I believed I could check the list length but it check each item length.