bq27441: Make status() private and review naming.

[nedseb]

Sub-issue of #79.

Context

The BQ27441 status() method returns the CONTROL_STATUS word (sealed state, shutdown mode, etc.), not a data-ready register like the other drivers. Its only caller is sealed().

This creates two problems:

1. status() is public but only used internally
2. The name status() has a different meaning than in sensor drivers (data-ready vs control state)

TODO

• Rename status() → _control_status() to reflect its actual purpose and avoid confusion with the sensor status() convention
• Update sealed() to call _control_status()
• Update tests if any reference status()

[nedseb]

Merged via PR #149.