Remove dependency on bcmath or gmp

[superdav42]

wp multisite waas uses the hashid library which requires bcmath or gmp extensions. Most hosts probably have them but since they are not required by wordpress we shouldn't assume they are available. It should be possible to add a polyfill alternative.

[superdav42]

When looking at dependencies there's 2 others that are not fully compatible with PHP 8.4. "remotelyliving/php-dns" and "rakit/validation". Both have newer versions that are compatible with PHP 8.4 but not PHP 7.4. We should see if these dependencies are really needed

[superdav42]

Plan to resolve:

• Search the codebase for usages of bcmath and gmp (e.g., bc*, gmp_*) and list call sites with context.
• Replace with small, well-tested pure-PHP helpers for required operations (e.g., arbitrary-precision add/sub/mul/div, comparisons) within a WP_Ultimo\Utils\Math utility, falling back to extensions when available.
• Scope: only implement the specific operations actually needed by WP Ultimo (e.g., currency math, proration), not a general big-number library.
• Ensure identical behavior for rounding/precision as before; add unit tests around current monetary and discount calculations to validate parity.
• Remove hard extension checks and guard code paths via feature detection.

Question:

• Do we only need high-precision decimal operations for currency and proration, or are there other code paths (tokens, hashing, etc.) relying on bcmath/gmp? Any examples welcome.