[Feature](lance) Support additional Lance and Arrow data types

Parent

Tracked by #66340. Core Arrow and Lance scalar, nested, and vector types were introduced by #65730.

Scope

Lance Blob v2.
Arrow JSON Extension.
Lance BFloat16 Extension.
Arrow null.
Arrow duration.
Preserve extension metadata and define Doris type mappings and unsupported-column behavior.

Completion criteria

FE schema conversion and BE Arrow deserialization are implemented safely.
Unit and regression tests cover schema discovery, projection, nullability, and malformed input.
User documentation describes mappings, precision, and limitations.
Representative datasets for every listed type are verified.

Partial completion — 2026-09-30

#67325 merged FE/BE mappings and tests for Arrow/Lance JSON, BFloat16, Null, and Duration into branch-4.1; #67921 added nested nullable Arrow Null support and regression coverage. Both PRs have successful recorded External Regression statuses. English and Chinese mapping/precision/limitation documentation is synchronized by merged apache/doris-website#4182.

These four type items are complete. JSON requires compatible extension storage, BFloat16 widens to FLOAT, Duration preserves the signed count in its declared unit, and unsupported extensions/storage combinations remain rejected. The current catalog documentation still explicitly lists Lance Blob v2 as unsupported.

Keep this issue open for Blob v2. The general extension-metadata and all-types completion criteria remain unchecked because they include that outstanding type. Completion on branch-4.1 satisfies the parent tracker's branch criterion; this audit does not claim a fresh test run.