* Complete PHPStan Level 6
Fix https://github.com/FreshRSS/FreshRSS/issues/4112
And initiate PHPStan Level 7
* PHPStan Level 6 for tests
* Use phpstan/phpstan-phpunit
* Update to PHPStan version 1.10
* Fix mixed bug
* Fix mixed return bug
* Fix paginator bug
* Fix FreshRSS_UserConfiguration
* A couple more Minz_Configuration bug fixes
* A few trivial PHPStan Level 7 fixes
* A few more simple PHPStan Level 7
* More files passing PHPStan Level 7
Add interface to replace removed class from https://github.com/FreshRSS/FreshRSS/pull/5251
* A few more PHPStan Level 7 preparations
* A few last details
* Keep the user on login page on failure
* Show an error if username already exists
* Check the password format in the backend
* Return a better message if username is invalid
* Add a title to the login page
* wip: Improve look of login and register pages
* Set a capital M in username help message
On the registration page, username tip started with a minuscule, while
the password tip started with a capital.
* Change message if username is taken
* Extract hashPassword method from userController
* Extract and refactor fever key-related methods
* Move update of API password to dedicated action
* Simplify the controller by refactoring feverUtil
* Add locales