feat: remove retired Lucy model IDs

[AdirAmsalem]

Summary

• remove lucy-2 from realtime and video model definitions
• remove retired Lucy 2 SDK aliases (lucy_2_rt, lucy-2-v2v)
• update examples, playground, and tests to use lucy-2.1

Test plan

• .venv/bin/python -m pytest tests/test_models.py tests/test_realtime_unit.py
• .venv/bin/ruff check .

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Note

Low Risk
Primarily removes deprecated/retired model identifiers and updates references/tests; main risk is a breaking change for users still passing lucy-2 or its old aliases.

Overview
Removes retired lucy-2 model IDs from the SDK’s realtime/video model unions and _MODELS registry, and drops legacy alias mappings for lucy_2_rt and lucy-2-v2v.

Updates sample code, playground model lists, token docs/examples, and unit tests to use lucy-2.1 instead (including updated expected model dimensions/FPS and queue submission fixtures).

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