chore: major code cleanup and type safety using phpstan

tests/BusProNet/DataLoader/TravelDataLoaderTest.php

@@ -29,7 +29,7 @@ class TravelDataLoaderTest extends TestCase
 </reisen>';
 
         $filesystem = $this->createMock(FilesystemOperator::class);
-        $filesystem->expects($this->once())
+        $filesystem->expects(self::once())
             ->method('read')
             ->with('test_file.xml')
             ->willReturn($xmlContent);
@@ -45,7 +45,7 @@ class TravelDataLoaderTest extends TestCase
         $expectedTravel->label = 'Davos - Sportclub Waldschlössli';
         $expectedTravel->priceFrom = 534.2;
 
-        $travelParser->expects($this->once())
+        $travelParser->expects(self::once())
             ->method('parse')
             ->willReturn($expectedTravel);
 
@@ -54,12 +54,12 @@ class TravelDataLoaderTest extends TestCase
 
         $travel = $loader->loadById(11478, null, 'test_file.xml');
 
-        $this->assertInstanceOf(Travel::class, $travel);
-        $this->assertEquals('DPWMP060125', $travel->code);
-        $this->assertEquals('F', $travel->type);
-        $this->assertInstanceOf(\DateTimeImmutable::class, $travel->dateFrom);
-        $this->assertInstanceOf(\DateTimeImmutable::class, $travel->dateTo);
-        $this->assertEquals('Davos - Sportclub Waldschlössli', $travel->label);
-        $this->assertEquals(534.2, $travel->priceFrom);
+        self::assertInstanceOf(Travel::class, $travel);
+        self::assertEquals('DPWMP060125', $travel->code);
+        self::assertEquals('F', $travel->type);
+        self::assertInstanceOf(\DateTimeImmutable::class, $travel->dateFrom);
+        self::assertInstanceOf(\DateTimeImmutable::class, $travel->dateTo);
+        self::assertEquals('Davos - Sportclub Waldschlössli', $travel->label);
+        self::assertEquals(534.2, $travel->priceFrom);
     }
 }