Convert the four simple-type-pass compile checkers to located findings so
each error attaches to its own declaring node instead of the schema root
(#169): a list whose item type is itself a list or a union containing a
list and a list declaring both or neither of itemType/inline simpleType
(simpleTypeVarietyFindings), an empty union, a simpleType restriction whose
base resolves to a complex type (simpleTypeBaseNotComplexFindings), an
itemType/memberType referencing a type final for list/union derivation
(simpleTypeFinalFindings), and an attribute typed by a complex type
(attributeTypeMustBeSimpleFindings).
Each predicate, traversal order, and reason string is unchanged; only the
location each finding carries differs, from the schema root to the
offending list, union, restriction, or attribute node. The four checkers
had exactly one caller each (their compile-rule dispatch), so each is
renamed in place and the .unlocated wrap dropped, leaving no dead wrapper.
Adds a located-diagnostics test per checker in a new suite kept within the
type-body budget.
