Refactor shaker backend API to use start_shaking

[j0nch]

Summary

This PR refactors shaker backend naming to make backend semantics explicit and consistent:

• Backend API now uses start_shaking(...) + stop_shaking(...).
• Frontend Shaker.shake(..., duration=None) remains the orchestration entrypoint for users.
• Deprecated backend shake(...) aliases are kept in concrete implementations for compatibility.

Motivation

Previously, backend shake(...) semantically meant "start shaking", while frontend Shaker.shake(...) also handled optional duration/stop behavior. This naming overlap was ambiguous.

Using start_shaking(...) at backend level makes intent clearer and aligns with stop_shaking(...).

Changes

Shaker backend contract

• pylabrobot/shaking/backend.py
  • ShakerBackend now defines abstract start_shaking(speed: float).

Shaker frontend

• pylabrobot/shaking/shaker.py
  • Shaker.shake(...) now calls backend.start_shaking(...).
  • Frontend remains the single user-facing orchestration method (duration support unchanged).

Chatterbox backend

• pylabrobot/shaking/chatterbox.py
  • Implements start_shaking(...).
  • Adds deprecated shake(...) alias with warning, forwarding to start_shaking(...) for migration parity with hardware backends.

Heater-shaker backend implementations aligned

• pylabrobot/heating_shaking/hamilton_backend.py
  • Implements start_shaking(...).
  • Keeps deprecated shake(...) alias forwarding to start_shaking(...).
• pylabrobot/heating_shaking/inheco/thermoshake_backend.py
  • Implements start_shaking(...).
  • Keeps deprecated shake(...) alias forwarding to start_shaking(...).
• pylabrobot/heating_shaking/bioshake_backend.py
  • Implements start_shaking(...)
  • Keeps deprecated shake(...) alias forwarding to start_shaking(...).

Backward compatibility

• Existing backend calls to .shake(...) continue to work in concrete backends via deprecation aliases.
• New code should call .start_shaking(...) at backend level.

Testing / validation

Executed:

python -m pytest -q pylabrobot/shaking/shaker_tests.py pylabrobot/heating_shaking/heater_shaker_tests.py