fix: Multisite table names, dbDelta schemas, and migration guards

[mwenell]

Summary

This PR improves WordPress Multisite support for Tutor LMS 4.0.4. It fixes incorrect global table prefixing (users / usermeta), dbDelta schema issues on network activation, Site Editor REST errors when cart tables are missing, and migration cron fatals on subsites without Tutor tables.

I have made this fix because Tutor LMS was crashing when Wordpress was makingg API calls related to user specific patterns in Gutenberg editor (templates). With these fixes I can use the Tutor LMS in my multisite Wordpress. However, I have not tested everything, only my own things are now working fine.

I hope that you could add these updates in your next update -> I do not need to keep updateing by myself my own multisite version.

I have posted in Wordpress plugin forum (Tutor) at https://wordpress.org/support/topic/multisite-support-has-bugs/

This changes are done by using Cursor and AI.

Problems addressed

1. Global tables on subsites — QueryHelper::prepare_table_name() produced invalid names like wp_7_usermeta and wp_7_wp_users instead of wp_users / wp_usermeta.
2. Plugin activation / dbDelta — CREATE TABLE schemas used patterns dbDelta mishandles (unnamed INDEX, inline -- comments, TEXT defaults, FOREIGN KEYs with database-global constraint names on Multisite).
3. Site Editor / Patterns — REST the_content triggered cart/checkout DB queries on blogs without ecommerce tables.
4. Cron migrations — quiz_attempt_migrator fatals when wp_N_tutor_quiz_attempts does not exist on network-activated subsites.

Approach

Centralized fix in QueryHelper::prepare_table_name() plus minimal related call sites. No fake per-blog users/usermeta tables. Single-site behavior intended unchanged.

Documentation

See UPSTREAM_FIXES.md in this PR for root cause, file list, and verification steps.

Test plan

• Multisite subsite: no queries to wp_N_users, wp_N_usermeta, wp_N_wp_users
• Tutor::create_database() on a subsite without duplicate FK / empty KEY errors
• Site Editor Patterns reload without missing tutor_carts fatals
• quiz_attempt_migrator cron on blog without Tutor tables does not fatal
• Single-site: table naming unchanged

Environment

• WordPress 7.0.2 Multisite
• Tutor LMS 4.0.4
• Custom prefix example: main wp_, subsite wp_7_

Happy to adjust based on your coding standards or split into smaller PRs if preferred.