Add unit tests for EV and PV HPXML parsing #225

Context

The new parse_ev_from_vehicle() and parse_pv() functions in ochre/utils/hpxml.py lack dedicated unit tests. These functions handle multiple input combinations (BEV vs PHEV, different charger levels, missing fields, inverter configurations, etc.) that should be verified.

Suggested Approach

• Add test cases for parse_ev_from_vehicle(): BEV vs PHEV, Level 1 vs Level 2 charger, missing battery capacity, multiple vehicles
• Add test cases for parse_pv(): various azimuth/tilt values, missing inverter info, capacity extraction
• Add test cases for parse_ev_from_mel(): legacy MEL-based EV fallback path

References

• ochre/utils/hpxml.py (lines ~1583-1757)
• PR Features to support OCHRE workflow in ResStock #205 review comment from @jmaguire1