fix(extractors): suppress SoC kWh warning spam for non-EV vehicles

[nanomad]

Summary

• extract_soc_kwh now returns None silently when charge_status is None
• Non-EV vehicles (e.g., ZP22 series) pass charge_status=None on every poll, causing a spurious WARNING: Could not extract a valid SoC kWh on every cycle
• The WARNING is preserved for EVs where charge status is present but kWh derivation genuinely fails

Test plan

• 293 existing tests still pass (poetry run pytest tests --cov)
• mypy clean
• Manual: non-EV vehicle no longer emits SoC kWh WARNING on each poll