Upgrade project to PHP 8.3, add PHPStan, upgrade almost every dependency (#36)

* start updating to PHP 8.3

* taking off!

Co-authored-by: ErickSkrauch <erickskrauch@yandex.ru>
Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* dropped this

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* migrate to symfonymailer

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* this is so stupid 😭

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* ah, free, at last.

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* oh, Gabriel.

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* now dawns thy reckoning.

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* and thy gore shall GLISTEN before the temples of man.

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* creature of steel.

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* my gratitude upon thee for my freedom.

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* but the crimes thy kind has committed against humanity

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* Upgrade PHP-CS-Fixer and do fix the codebase

* First review round (maybe I have broken something)

* are NOT forgotten.

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

* Enable parallel PHP-CS-Fixer runner

* PHPStan level 1

* PHPStan level 2

* PHPStan level 3

* PHPStan level 4

* PHPStan level 5

* Levels 6 and 7 takes too much effort. Generate a baseline and fix them eventually

* Resolve TODO's related to the php-mock

* Drastically reduce baseline size with the Rector

* More code modernization with help of the Rector

* Update GitLab CI

---------

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>
Co-authored-by: ErickSkrauch <erickskrauch@yandex.ru>

api/tests/unit/modules/internal/models/PardonFormTest.php

@@ -8,7 +8,7 @@ use common\models\Account;
 
 class PardonFormTest extends TestCase {
 
-    public function testValidateAccountBanned() {
+    public function testValidateAccountBanned(): void {
         $account = new Account();
         $account->status = Account::STATUS_BANNED;
         $form = new PardonAccountForm($account);
@@ -22,10 +22,10 @@ class PardonFormTest extends TestCase {
         $this->assertSame([E::ACCOUNT_NOT_BANNED], $form->getErrors('account'));
     }
 
-    public function testPardon() {
+    public function testPardon(): void {
         /** @var Account|\PHPUnit\Framework\MockObject\MockObject $account */
         $account = $this->getMockBuilder(Account::class)
-            ->setMethods(['save'])
+            ->onlyMethods(['save'])
             ->getMock();
 
         $account->expects($this->once())