ConnectedHardware → Protocol; rename current class to ConnectedManipulator

Problem

ConnectedTwistBase and ConnectedWholeBody both inherit from ConnectedHardware and override .adapter with # type: ignore[override] — a Liskov Substitution Principle violation mypy is being told to swallow. Parent claims .adapter -> ManipulatorAdapter; subclasses return totally different types. Latent crash: any code that reaches connected.adapter.set_control_mode(...) on a non-manipulator instance fails at runtime.

The current ConnectedHardware class is itself misnamed — its read_state / write_command are manipulator-specific (POSITION/VELOCITY/TORQUE mode switching, read_joint_positions(), etc.). The "Hardware" name only fit when manipulators were the only kind.

Proposed fix

1. Make ConnectedHardware a @runtime_checkable Protocol with the truly common surface: hardware_id, joint_names, dof, component, read_state(), write_command(), disconnect(). .adapter is intentionally not on the Protocol — concrete classes expose it with their own adapter type; callers must narrow.
2. Rename current concrete ConnectedHardware → ConnectedManipulator.
3. ConnectedTwistBase and ConnectedWholeBody stop inheriting; satisfy the Protocol structurally as siblings.

Protocol (not ABC) because the three classes share almost no implementation — _initialize_last_commanded and write_command are fundamentally different per kind.

Why it matters

• Removes a known latent runtime crash.
• Drops three # type: ignore[override] from the codebase, no replacements.
• Names match reality; new hardware types just implement the Protocol.

Origin: PR #1954 review comment from @paul-nechifor.

Synced from DIM-832 by summer