[rset] fix infinite recursion introduced in c1eb5a676c80 The mechanism to avoid loops in c1eb5a676c80 "[rset] Always complete attribute/relation caches in ResultSet.get_entity" breaks down: we would loop forever if two entities that were already in the cache were linked by a relation with ? or 1 cardinality in both directions. To avoid that, keep a set of already-considered columns. Related to #9942503.

[MESSAGES CONTROL]
disable-msg = C0301

[VARIABLES]
# Enable / disable this checker
enable-variables = yes
additional-builtins = _, display_name

[BASIC]
required-attributes=
attr-rgx = (w|[a-z_][a-z0-9_]{2,30})
variable-rgx = (w|[a-z_][a-z0-9_]{2,30})$
argument-rgx = (w|[a-z_][a-z0-9_]{2,30})$

[TYPECHECK]
generated-members=debug,info,notice,warning,error,critical,exception