[entities] Fix backward compat of IDublinCore adapter wrt dc_long_title `entity.dc_long_title()` used to fallback to `dc_title()`, and most entity types were relying on this, thus only implementing the later. Since introduction of the IDublinCore adapter, if one call `entity.dc_long_title()` on an entity that only implements `dc_title()`, it will retrieve the adapter which will then call its own `title()` method instead of the `dc_title()` method of the entity as expected. Fix this by calling instead `entity.dc_title()` which will eventually kick in the backward compat layer if necessary.

[web] Do not try to rmtree symlinks in rmtreecontent() There is a symlink in data directory (created by generate_static_dir() method) and trying to rmtree() it will fail with an OSError. So we unlink() it instead.

[pkg] Version 3.25.0rc3

[test] Stop using lgc.testlib

Fix some flake8 errors

[sources] Turn classmethod into standard method No need for a class method and easier to get proper logger including source's name.

[test] Add some tests for hooks.syncsources for parts which are not located in some source's check_config / check_urls method.