lis2mdl: Make status() private.

[nedseb]

Sub-issue of #79.

Context

The status() method returns the raw STATUS register value, which is a hardware implementation detail. Public API should use data_ready() and per-channel *_ready() methods instead.

TODO

• Rename status() → _status() in device.py
• Update all internal callers (data_ready(), *_ready(), _ensure_data(), etc.)
• Update tests referencing status()

[nedseb]

Merged via PR #149.