refactor(lerobot): type metadata at import boundary

[victorwon2001]

Summary

Parse LeRobot meta/info.json once into frozen internal dataset, episode, video-window, and numeric-feature values while keeping the downloaded JSON cache unchanged. Conversion now consumes those typed values directly, with existing paths, schemas, provenance, manifest contents, revision namespacing, and video-cache behavior preserved.

Why

LeRobot feature specifications remained as nested raw dictionaries after the external JSON boundary, allowing metadata interpretation to be repeated later in discovery and conversion. Moving supported validation and normalization to the boundary makes invalid supported shapes unrepresentable internally without expanding dtype/rank support or changing canonical output behavior.

Fixes #320

Validation

• uv run ruff check --fix — passed
• uv run ruff format — passed
• uv run ty check — passed
• uv run pytest -q tests/test_lerobot_converter.py — 47 passed
• uv run pytest -q — 1452 passed, 6 skipped
• git diff --check — passed

Checklist

• I added or updated outcome-focused tests for changed business logic.
• I updated documentation for changed behavior, flags, formats, or requirements. Not applicable: this keeps the public behavior and formats unchanged.
• I ran uv run ruff check --fix, uv run ruff format, and uv run ty check.
• I ran the relevant pytest suite.
• I did not add recordings, generated media, credentials, private URLs, or runtime artifacts.
• I preserved stored-data compatibility or documented an explicit version change.

[github-actions]

👋 Hi @victorwon2001 — thanks for the contribution! To keep starter issues available
for other contributors and give every pull request a real review, we accept
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You already have #380 open, so this one is being closed automatically.
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