fix(pageFilters): Handle invalid stats period gracefully

[sentry]

This PR addresses JAVASCRIPT-3925, an issue where the application would crash with an "Error: Invalid stats period" when an unvalidated period string was passed to `parseStatsPeriod`.

The root cause was that pageFilters.datetime.period, which can originate from localStorage or the URL, was not validated against STATS_PERIOD_REGEX before being used by parseStatsPeriod. If the period was malformed or stale, parseStatsPeriod would throw, leading to a page crash.

The solution involves:

1. Exporting STATS_PERIOD_REGEX from static/app/components/timeRangeSelector/utils.tsx.
2. In static/app/components/pageFilters/actions.tsx, before calling parseStatsPeriod, pageFilters.datetime.period is now checked against STATS_PERIOD_REGEX. If the period is invalid, it is reset to the defaultDatetime.period (e.g., "14d") instead of allowing parseStatsPeriod to throw. This ensures the page loads with a valid default time range.

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Fixes JAVASCRIPT-3925

_{Comment @sentry <feedback> on this PR to have Autofix iterate on the changes.}