feat(tlabel): add TLabel format reader/writer

[liesliy]

What

Adds read/write support for TLabel tactile annotation files as a Forge format.

TLabel is an open schema for tactile sensor data (GelSight, PaXini, Daimon, etc.) with a 14-dimensional semantic annotation standard. This PR allows users to:

# Convert: LeRobot + tactile labels → merged dataset
forge convert /data/lerobot --tactile-annotations /data/tactile/ --tactile-format tlabel -o /data/merged --output-format lerobot-v3

# Inspect a .tlabel file
forge inspect /data/episode_001.tlabel --format tlabel

Changes

• forge/formats/tlabel/reader.py — reads .tlabel JSON files into Forge Episodes (tactile dims stored in Frame.extras["tlabel.schema_v2"])
• forge/formats/tlabel/writer.py — writes Forge Episodes back to .tlabel format
• forge/formats/__init__.py — registers the new format
• tests/test_tlabel.py — reader/writer/roundtrip tests

Design Notes

• No hard dependency on tlabel package — the reader/writer work directly with .tlabel JSON files. The tlabel PyPI package is only needed for schema validation.
• Tactile data in Frame.extras — Forge's canonical fields (state/action/images) are for proprioception. Tactile sensing goes to extras["tlabel.*"], keeping the core model clean.
• Zero-impact if unused — wrapped in try/except ImportError like other formats.

Context

I opened Issue #39 requesting this feature. Happy to submit the implementation directly to save you time.

If this doesn't fit the project's direction or needs changes, no worries at all — just let me know and I'll adjust. 😊

cc @arpitg1304