salesforce_auth 9.0.0

First release of the 6.0.x branch. Adds Drupal 10 and 11 support and fixes several errors that stopped Salesforce login and logout from working.

Requirements
- Drupal 10 or 11 (Drupal 8 and 9 are no longer supported; use the 5.0.x branch for those).

Important: after updating
- Run database updates (drush updb) and clear caches (drush cr).
- The module's permission is renamed from "administer netauth" to "administer salesforce_auth". The database update moves existing roles to the new permission automatically.

Fixes
- Logout no longer fails while the module is enabled. Logging out now also revokes the Salesforce access token.
- The "Log in with Salesforce" button now appears on the login form again.
- The Salesforce callback page (/salesforce/callback) works again. It previously failed because of a removed service, a misspelled method and an invalid return value.
- Fixed classes declared in the wrong namespace, which stopped Salesforce query and object classes from loading.
- Replaced code removed in Drupal 9 and later (db_delete, db_table_exists, Unicode::strlen, REQUEST_TIME, drupal_set_message, drupal_goto, variable_get).
- Replaced user_load_by_mail(), deprecated in Drupal 11.4.
- Fixed PHP 8.2–8.4 deprecation warnings.
- Removed the unused hook_init() and invalid library entries.
- Corrected the error message for an invalid login URL on the settings form.

Issues fixed
- #3297992: Automated Drupal 10 compatibility fixes