Fix recursive directory removal across platforms

Add FileSystem::dirRemoveAll() to normalize trailing separators and use the non-throwing std::filesystem::remove_all overload.

Migrate ecode and unit-test cleanup call sites to the centralized helper, preventing Haiku from crashing when removing directories with trailing slashes during shutdown.

src/tests/unit_tests/stringsoperations_tests.cpp

@@ -55,10 +55,7 @@ class ScopedTestDirectory {
   public:
 	explicit ScopedTestDirectory( std::filesystem::path path ) : mPath( std::move( path ) ) {}
 
-	~ScopedTestDirectory() {
-		std::error_code error;
-		std::filesystem::remove_all( mPath, error );
-	}
+	~ScopedTestDirectory() { FileSystem::dirRemoveAll( mPath.string() ); }
 
   private:
 	std::filesystem::path mPath;