[Tests] Isolate ApplicationFileProcessorTest cache dir to survive parallel chunk clears

[TomasVotruba]

ApplicationFileProcessorTest asserts real cache persistence (save then load) against the shared cache directory sys_get_temp_dir() . '/rector_cached_files'. Under fastunit -tia, test chunks run as parallel processes that all share that one directory, and FileCacheStorage::clear() deletes the whole directory:

public function clear(): void
{
    FileSystem::delete($this->directory);
}

So a sibling chunk can wipe this test's cache entry between the save and the load, making hasFileChanged() find nothing and return true ("be defensive and assume it's changed"). The three cache-scope tests then fail with Failed asserting that true is false. — non-deterministically, depending on chunk timing.

Fix

Bind a dedicated cache directory for this test only, so no other chunk's clear() can touch it:

     protected function setUp(): void
     {
         parent::setUp();

+        // isolate the cache directory to this test - the default directory is shared across all
+        // parallel test chunks, and FileCacheStorage::clear() deletes the whole directory, so a
+        // sibling chunk can wipe this test's cache between save and load and flip the assertions
+        $rectorConfig = self::getContainer();
+        SimpleParameterProvider::setParameter(
+            Option::CACHE_DIR,
+            sys_get_temp_dir() . '/rector_test_application_file_processor'
+        );
+        $rectorConfig->singleton(
+            Cache::class,
+            static fn (Container $container): Cache => $container->make(CacheFactory::class)->create()
+        );
+
         $this->applicationFileProcessor = $this->make(ApplicationFileProcessor::class);
         $this->changedFilesDetector = $this->make(ChangedFilesDetector::class);
     }

The Cache singleton is rebound so it is rebuilt from the isolated directory (it is otherwise created once per process from the default directory). Test-only change.