Fix code style and update test structure

- Rename tests/cases to tests/Cases for PSR-4 compliance
- Add constant visibility and void return type hints
- Remove unused imports
- Remove obsolete kodiak and coveralls configs

Author: f3l1x

.github/.kodiak.toml

@@ -17,7 +17,6 @@
 use Nette\DI\Definitions\Statement;
 use Nette\Schema\Expect;
 use Nette\Schema\Schema;
-use stdClass;
 
 /**
  * @property-read object{
@@ -43,7 +42,8 @@
  */
 class Atlantic18BehaviorExtension extends CompilerExtension
 {
-	const TAG_NAME = 'nettrine.extensions.atlantic18.listener';
+
+	public const TAG_NAME = 'nettrine.extensions.atlantic18.listener';
 
 	public function getConfigSchema(): Schema
 	{
@@ -136,7 +136,7 @@ public function loadConfiguration(): void
 		}
 	}
 
-	public function beforeCompile()
+	public function beforeCompile(): void
 	{
 		$builder = $this->getContainerBuilder();