TIMESTAMP_NTZ type support for Velox backend

### Description

Create this to track the support for TIMESTAMP_NTZ type in Velox backend. Velox has presto `TimestampWithTimeZoneType`, but it's semantic is different with Spark's.

The issue names the Velox backend and Spark's TIMESTAMP_NTZ semantics but no files, tests, or entry points. Start by locating the backend's timestamp type handling and the existing Spark and Velox timestamp mappings. Done means TIMESTAMP_NTZ is supported with semantics distinct from Velox's TimestampWithTimeZoneType, with coverage in the relevant tests.

Written by the indexing model from the issue text.