Update v.2.5.0 — caching, cron and order currency fixes

A maintenance release focused on how FOX behaves behind a page cache, and on order editing in wp-admin.

• New caching mode: browser key instead of a cookie. With Storage set to Transient and the cache option enabled, the plugin now keeps a random key in the browser's localStorage rather than setting a cookie on every first visit. A cookie on the first request makes aggressive caches — Cloudflare APO in particular — treat every page as dynamic and bypass the cache site-wide. Every other storage combination behaves exactly as before.
• Fixed the cron scheduler. is_attached() returned false not only when the hook was missing, but also when the stored recurrence differed from the configured one. Whenever those two disagreed, every page request re-attached the event and pushed the next run a full interval into the future, so automatic rate updates could stall indefinitely.
• Fixed inflated order totals in currencies that use a comma as the decimal separator. Saving or editing an order in the wp-admin order editor could multiply the amount.
• Fixed the currency symbol on HPOS orders. After saving order items the base currency symbol was shown instead of the order's own currency.