feat: add Vertica adapter support

[Albayrakengin]

What

Adds Vertica to the supported adapters, mirroring the sqlserver contribution
pattern for adapters whose SQLGlot dialect name differs from the dbt
adapter_type.

Why these decisions

• Vertica maps to SQLGlot postgres. SQLGlot has no native Vertica dialect.
  dbt-vertica projects emit adapter_type: "vertica" in manifest.json, and Vertica
  SQL/identifier behaviour is close enough to reuse the existing postgres parsing
  path.
• self.adapter_type is tracked separately from self.dialect. For remapped
  adapters (sqlserver → tsql, vertica → postgres), quoted-column case
  sensitivity must follow adapter semantics, not the mapped SQLGlot dialect alone.
  _build_quoted_columns_lookup therefore checks adapter_type.
• DialectInfo("vertica", "lower", True, "vertica", sqlglot_dialect="postgres"). Vertica uses 3-part identifiers and double-quoted,
  case-sensitive identifiers like Postgres. Unquoted identifiers are lowercased.

Fixture generation

tests/test_data/vertica/ is derived from the existing postgres jaffle_shop
fixture with metadata.adapter_type set to "vertica". Happy to regenerate from a
real dbt-vertica project if maintainers prefer native artifacts.

Verification

• pytest tests/test_extractor.py::test_adapter_type_detection_vertica -q
• pytest tests/test_extractor.py::test_adapter_type_detection_sqlserver -q
• pytest tests/test_extractor.py::test_vertica_quoted_columns_preserve_case -q
• pytest tests/test_dialect_matrix.py -q
• pytest tests/ -q