Woocommerce Subscriptions

## What's New
- Background Migration Progress Triggers: Integrated a background notice system that surfaces real-time tracking updates while existing *All Products for Subscriptions* product metadata scales into the core database structure, followed by an automated completion confirmation.
- Block Layout Cart Adjustments: Refined upfront payment notations inside the block-based Cart environment to perfectly mirror the native Checkout block presentation, outputting cleaner, conversational billing strings (e.g., "$10.00 due today" instead of "Due today $10.00").
- Unified Shortcode Theme Parity: Upgraded legacy shortcode cart and checkout interfaces to preserve styling alignments introduced by the modernized block layers—isolating sign-up fees and free trials onto distinct labeled lines and calculating precise subtotals for items with immediate due-today costs.
- Developer Hook Implementation: Added a new `woocommerce_subscriptions_pre_product_subscription_scheme_mode` architectural filter, permitting developer integrations to programmatically alter or short-circuit a product's resolved subscription scheme prior to reading raw database meta.

## Bug Fixes
- Preserved Plans During Sync: Resolved a data-state drift issue where active inventory items temporarily reverted to static "one-time only" structures while the background database engine was busy building active processing batches.
- Core Verification Log Flood: Addressed a performance framework bug that generated repetitive "Invalid plugin file" errors inside administrative logging tools on every backend page load sequence after the *All Products for Subscriptions* system was merged.
- Sign-Up Fee Tax Discrepancies: Fixed a pricing display suffix error where front-end sign-up fees missed localized store tax declarations (e.g., "incl. VAT"), resolving user confusion over whether initial upfront charges were tax-free.
- PHP 8 Cart Filter Exception: Rectified an execution crash occurring under PHP 8 runtime environments when external plugin hooks utilizing `woocommerce_add_cart_item_data` mistakenly passed non-array type arrays during cart additions.