Address 3.x issues

Problem/Motivation

There are lots of small errors that need to be addressed, but existing patches overlap too much to be applied together.

• https://www.drupal.org/project/eat/issues/3393262 📌 Automated Drupal 10 compatibility fixes Needs review
• https://www.drupal.org/project/eat/issues/3391125 🐛 Undefined variable $etid Needs review
• https://www.drupal.org/project/eat/issues/3225246 🐛 Notice: Undefined variable: i in Drupal\eat\Eat::matchupEntitiesToSet() Active
• https://www.drupal.org/project/eat/issues/3384774 🐛 undefined function - eat_load_all_for_entity() Active

Steps to reproduce

Install the module at 3.x with Drupal 9 or Drupal 10. Notice several errors including undefined variables, array mismatches, and code quality issues.

Proposed resolution

Address all of these outstanding issues.

Remaining tasks

Testing and working toward a new release.