[Caching] Drop MemoryCacheStorage, always use FileCacheStorage

[TomasVotruba]

Previously CacheFactory picked MemoryCacheStorage in CI and FileCacheStorage elsewhere. The memory storage was meant to skip "wasted IO" of writing cache files that CI never reads again.

Benchmark on rector's own src/ (491 files, full rule set, --dry-run, PHP 8.4) shows no speed gain from the memory path:

Mode	Wall	Peak RSS	Cache files
FILE cold (empty cache)	23.4 s	301 MB	484 written
FILE warm	3.3 s	178 MB	reused
MEMORY (single run)	25–28 s	297 MB	0

Within a single run, MemoryCacheStorage is the same speed as FileCacheStorage cold (both do full analysis; the ~484 cache-file writes cost nothing next to analysis time). It just never persists, so every run stays cold. The only real win comes from the file cache on reruns (~7x faster, 3.3 s vs 23 s).

So the split added a whole storage class and a CiDetector branch for zero measurable benefit. This drops MemoryCacheStorage and always uses FileCacheStorage.

 public function create(): Cache
 {
-    // in CI the workspace is ephemeral and usually starts from scratch,
-    // so a file cache that is never read again is only wasted IO -> use faster in-memory cache
-    if (new CiDetector()->isCiDetected()) {
-        return new Cache(new MemoryCacheStorage());
-    }
-
     $cacheDirectory = SimpleParameterProvider::provideStringParameter(Option::CACHE_DIR);
     ...
     return new Cache(new FileCacheStorage($cacheDirectory, $this->fileSystem));
 }

[TomasVotruba]

Ref rectorphp/rector#9855