Search-space limit format

Categorical input limit values might be given as list or set literals.
Iterables containing mixed types should give a warning and be type inferred.

Start by locating the search-space handling entry point for categorical input limits. Trace how list and set literals are currently processed, then identify the tests covering iterable type handling. Done means list and set literals are accepted, while mixed-type iterables produce a warning and have their type inferred.

Written by the indexing model from the issue text.