Add master-next branch for rector comparison and scheduled testing
### Problem/Motivation
Introduces master-next branch to enable scheduled rector comparison runs and CI integration, supporting continuous analysis of rector coverage and improvements.
### Work items
- Commit(s): [a7ecbc6000](https://git.drupalcode.org/project/project_analysis/-/commit/a7ecbc6000f1), [a037777973](https://git.drupalcode.org/project/project_analysis/-/commit/a037777973aa), [1315209128](https://git.drupalcode.org/project/project_analysis/-/commit/131520912829)
### Credit
- Implemented by: @bbrala
---
*Filed retroactively as part of the Drupal 12 rector coverage effort. Closed as fixed; credit to be applied to the contributors listed above.*
*AI was used extensively to build this work and to file this issue. See [Dries Buytaert: AI-generated Rector rules for Drupal](https://dri.es/ai-generated-rector-rules-for-drupal) and [Björn Brala: Drupal Rector rules are config, not code. Mostly.](https://www.linkedin.com/pulse/drupal-rector-rules-config-code-mostly-bj%C3%B6rn-brala-vfpwe/).*
issue