Design unified Lance dataset reader for Hub/local video tasks

[Luodian]

Context

• Source PR: feat: integrate MINERVA benchmark with Lance-backed video mode and pipeline latency guidance #1121
• Maintainer feedback (kcz358): current LanceDB usage feels hardcoded for task-level integration and should evolve toward a more unified dataset format/reader (especially for Hub-hosted Lance datasets).

Problem

• Current MINERVA integration uses task-scoped resolver wiring via env vars and assumes task-specific schema conventions.
• This works for immediate integration but does not provide a reusable abstraction for future video tasks that want Lance-backed loading.

Goal

• Define a reusable Lance video reader abstraction that supports both local and HF Hub Lance URIs with clear schema contracts and fallback behavior.

Proposed plan

1. Introduce a generic Lance video reader utility under shared task/model utils.
2. Define and document a unified Lance video schema contract (required columns, optional metadata, blob handling, row id/address strategy).
3. Support pluggable source resolution (local path, hf:// URI) and cache strategy.
4. Add adapter hooks so tasks can opt in without duplicating resolver logic.
5. Add smoke tests covering local Lance + hf:// Lance read paths.

Acceptance criteria

• At least one existing task (MINERVA) migrated to the shared reader with no regression.
• Shared docs for Lance dataset format + runtime env/config knobs.
• End-to-end smoke validation for local and Hub-backed Lance inputs.

Notes

• Keep this as a follow-up architecture issue; PR feat: integrate MINERVA benchmark with Lance-backed video mode and pipeline latency guidance #1121 remains focused on delivering MINERVA Lance support safely.