Add HU-05 vector AST round-trip regression test - #1

Summary

• Adds explicit HU-05 regression coverage for vector AST round-trips in T-SQL 160 and 170.
• Verifies the AST -> generator -> re-parser -> generator cycle for seven vector scripts.
• Verifies that the generated output matches the existing baselines.

Validation

• Targeted HU-05 test: 1 passed, 0 failed.
• Full test suite: 1177 passed, 0 failed.
• Target framework: .NET 8.

Checklist

• Unit test added.
• Existing tests are passing.
• No production code changes were required.