feat(sqlserver): Part 6 — SQL type mapping and column builder

[axellpadilla]

Part of dbt-labs#15714 (upstream feature request). Depends on #1. Independent of #4, #5, #7 (can run in parallel).

Work items

• src/sql_types.rs — SqlServer arms wherever Fabric appears; verify each against actual SQL Server T-SQL types rather than assuming Fabric parity (real surface differences exist, e.g. VARCHAR/row-size limits)
• Metadata SQL type key arm (mirrors FABRIC_METADATA_SQL_TYPE_KEY)
• Review INTERVAL/ARRAY unimplemented arms — SQL Server also lacks both, likely directly reusable
• src/column/column_builder.rs — SqlServer arm, try build_postgres_like first per the guide's default recommendation

Full detail: dbt-sqlserver-v2-roadmap plan/02-implementation-steps.md §5.5 ("SQL type mapping", "Column builder")

PRs against sqlserver-v2-port in this repo, use Closes #<this issue>.