feat(runtime): add temporal VLA cache and adaptive chunking

[rylinjames]

Summary

• add conservative TemporalVLAReusePolicy for action-cache reuse decisions using age, language, phash, state, guard, and action-delta signals
• add AdaptiveChunkController and wire RTC execution horizon selection behind --adaptive-action-chunking
• feed real ActionGuard safety margins plus A2C2 correction/uncertainty telemetry into the next adaptive RTC decision
• add focused tests for temporal cache policy, adaptive chunking, guard margins, RTC signal wiring, and Typer runner compatibility

Validation

• PYTHONPATH=$PWD/src .venv/bin/python -m pytest tests/ -q -p no:cacheprovider -> 3055 passed, 82 skipped, 3 warnings
• .venv/bin/ruff check touched runtime/test files -> passed
• PYTHONPATH=$PWD/src .venv/bin/python -m py_compile edited runtime files -> passed

Notes

• src/tether/cli.py still has pre-existing Ruff debt outside this change; the new CLI flag compiles and is covered by the full test smoke.