Replace case/cond/if blocks with multi-clause function dispatch
and pattern matching in function heads across 9 modules:
- WeatherUnits: case to multi-clause unit_system/1, unit_labels via do_unit_labels/1
- PacketUtils: if to pattern match on %{"id" => id}, multi-clause threshold/callsign
- SetLocale: case to multi-clause extract_locale/1
- IPGeolocation: if/cond to pattern match on conn, binary prefix matching for private_ip?
- DeviceIdentification: cond to extracted pattern_matches?/2
- MobileChannel: cond to multi-clause do_callsign_match/2
- PacketProcessor: cond to dispatch_visibility/6 on {in_bounds, has_marker} tuple
- PacketManager: destructure packet_state in heads, multi-clause maybe_cleanup/3
- AprsSymbol: case/if to multi-clause get_table_id/1, normalize_symbol_code/1
- Handle both DateTime and NaiveDateTime structs from database
- Convert NaiveDateTime to UTC DateTime before formatting
- Add fallback for string timestamps
- Fixes FunctionClauseError when processing packets
