Add unit tests for AsterixDBSourceOpExec #6875

Task Summary

AsterixDBSourceOpExec at common/workflow-operator/src/main/scala/org/apache/texera/amber/operator/source/sql/asterixdb/AsterixDBSourceOpExec.scala has no spec (0% covered, ~104 uncovered lines). It builds SQL++ query strings with no JDBC, so the filter-condition builders (keyword / regex / geo / general), schema derivation, and query fragments are unit-testable.

Task Type

• Testing / QA