Fix coordinate parsing for events datafix: harden coordinate parsing and add tests

[AhmedAli58]

Problem: convert_lat and convert_lon can raise TypeError or IndexError for None, short, or malformed inputs, causing event loading to fail.

Solution: Introduce centralized coordinate parsing with input validation, safe fallback to np.nan, and debug logging for invalid inputs.

Tests: PYTHONPATH=. pytest

Compatibility: No breaking changes. Invalid inputs still resolve to np.nan, now without crashes.