Drop embed-allowed option, gone away for a long time

Never record undo information for session or data import for session, it may causes unlimited database size expansion while it makes no sense to undo this kind of changes. For data import, they are created programatically hence we may not want to undo this either.

[cwvreg] load registry using modules names instead of directories Introspect cubicweb, cubes and apphome using pkgutil to generate the full list of modules names for loading registries. Avoiding using bogus logilab.common.modutils.modpath_from_file().

[schema] load schema from modules names instead of directories Introspect cubicweb, cubes and apphome using pkgutil to generate the full list of modules names for loading the schema. Keep historical behavior and check if source .py file exists if a module is found using python bytecode file (.pyc and .pyo) Loading schema from apphome require apphome to be present in sys.path and that "schema" module resolve to a file located in apphome. Update migraction tests to explicitely update sys.path when loading schema from different apps, use a contextmanager for this so it's more readable. Require updated logilab-common and yams

[devtools/test] Skip qunit tests in case of timeout Follow-up on 87443f279b0f where other similar tests got adjusted not to fail (in particular in our CI environment).

[autoform] Avoid two calls to field.process_form for the same field in some cases when some entity is being created and data include non-inlined relations, the values for this relation are now stored for later usage, avoiding two calls to field's process_form method, which may be unexpected for custom fields. This has been discovered in saem_ref#f5444b1f9770. Reorganize imports in the test along the way.

[pyramid] Don't use unsafe_cnx_context_manager for write queries we may have clumsy error that hide previous problems on attempting to commit the transaction. Closes #16753531

Repair database wrt indexes / unique constraints * recreate indexes dropped by 3.23 migration (but it's still unclear why) * attempt drop remaining extra indexes (there may be a bunch of these on old instances) * warn about missing expected indexes Closes #16666137