Locale-aware number formatting in Distance/Temperature (fixes ungrouped odometer)

[MrL0]

What this does

Distance.Units.format and Temperature.Units.format build a NumberFormatter but never set numberStyle, so it defaults to .none — which applies no grouping separator and a hardcoded . decimal separator. Two user-visible consequences:

• Odometer / range render ungrouped: a 19,500 mi odometer shows as 19500 instead of 19,500.
• Half-degree Celsius (the maximumFractionDigits = 1 path) shows a hardcoded period: 22.5°C even in locales that use a comma.

Setting formatter.numberStyle = .decimal makes both locale-aware. maximumFractionDigits is still set afterward, so whole-number distances and Fahrenheit stay integer-only.

Because everything funnels through these two shared formatters, this fixes the odometer/range everywhere they appear (in-app, widget, Live Activity, Watch + complications, Trip view) with no call-site changes. It matters beyond the US — BetterBlue supports Hyundai US/CA/EU and Kia US/EU, and EU + French-Canada users use period/space grouping.

value	before	en-US	de-DE	fr-FR
19,500 mi odometer	19500 mi	19,500 mi	19.500 mi	19 500 mi
22.5 °C	22.5°C	22.5°C	22,5°C	22,5°C

Testing

swift test — 291 tests pass. Added testDistanceUnitsFormatGroupsThousands, which asserts grouping happens without pinning a specific separator, so it stays locale-independent across CI. Existing format assertions are unaffected (their values are < 1000, where no grouping appears).

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Drafted with AI assistance; verified locally with swift test.