Test explicit column mappings with name collisions

[elpete]

Closes #59

Issue review

Recommendation: 9/10 — preserve and test. An explicit column mapping must always win over an identically named physical column; otherwise an entity silently hydrates incorrect data. The regression is small and protects a fundamental mapping guarantee.

Reproduction note

The bug could not be reproduced on current next with qb@14.0.0-beta.3. The fixture maps a username property to first_name on a table that also has a real username column. Quick returns Eric from first_name, stores only the mapped first_name value internally, and does not hydrate the conflicting username column.

Implementation

• adds a focused entity fixture matching the issue’s collision shape
• verifies behavior through findOrFail and the generated public getter
• verifies the internal hydrated column is the explicit mapping

Validation

• focused AttributeSpec: 17 passed, 0 failed, 0 errors
• full Lucee 6 suite: 496 passed, 0 failed, 0 errors, 3 skipped
• box run-script format
• git diff --check

Uses qb@14.0.0-beta.3.