Switch "array_ref" and similar method names to "values"

Several resqpy methods cache and return an array of values. At the moment such methods typically have names ending "...ref" as a reminder that the resqpy object is holding on to a handle and that a new copy of the array will not be made if the method is called repeatedly.

It is suggested that such methods are renamed simply as "values" to be more consistent with some other packages.

No files or tests are identified. Start by inventorying resqpy methods whose names end in “ref” and cache or return arrays, then review their callers and existing naming patterns. Done means the affected methods consistently use “values” names.

Written by the indexing model from the issue text.