Expose electricity_charge and current_power in energy usage result

[nazamhussain]

What

This PR exposes the electricity_charge and current_power fields returned by
get_energy_usage, which were already present in the device response but not
mapped in the Rust response struct / Python bindings.

Why

Devices such as the P110 and P304M return cost and instantaneous power data
that is currently inaccessible via the Python API. This prevents users from
accessing billing-related information even though the device reports it.

Changes

• Added missing fields to EnergyUsageResult
• Updated Python bindings to expose the data
• No breaking API changes

Tested

• Verified against TP-Link P110
• Verified against TP-Link P304M (child plug)
• Confirmed values match raw device responses

Before

energy_usage:
{'local_time': '2025-12-29T00:23:09',
 'month_energy': 8455,
 'month_runtime': 3503,
 'today_energy': 56,
 'today_runtime': 23}

After

energy_usage:
{'current_power': 151171,
 'electricity_charge': [0, 0, 2238],
 'local_time': '2025-12-29T03:50:48',
 'month_energy': 8961,
 'month_runtime': 3710,
 'today_energy': 562,
 'today_runtime': 230}

[mihai-dinculescu]

Thank you for this PR.

I do agree that we should re-add current_power as quite a few people have been asking about it.

Can you please also add the two fields to https://github.com/mihai-dinculescu/tapo/blob/main/tapo-py/tapo-py/tapo/responses/energy_usage_result.pyi?

[mihai-dinculescu]

Any more info to add here? I.e. interval, range, etc.