walletCompactTimeFormat function
The activity/parked rows' compact date+time (MMMd + jm, e.g. "Jun 24,
3:45 PM"), locale-aware and memoized per locale (#317 — the old per-widget
statics froze to Intl.defaultLocale, an en-US time inside a ru sentence).
ONE factory shared by every row surface so the idiom can't drift.
Implementation
DateFormat walletCompactTimeFormat(String locale) => _compactTimeFmts
.putIfAbsent(locale, () => DateFormat.MMMd(locale).add_jm());