Keep directory discovery metadata in temporary jobs

Directory folder and file-list indices are only needed while initializing
descriptions and their cache. Replace the persistent lcPieceData fields
with local jobs holding the selected file info, source folder and change
flag. Workers update independent jobs, and cache writing uses their
timestamps after all workers finish.

Pass the discovered paths to alias classification so it opens the selected
source directly without reconstructing paths from asset bookkeeping.
Move include-free piece member defaults into the header and zero-initialize
the filename and description arrays there.

Validated with a warning-free Qt 6.10 Debug build, 58 offscreen lifecycle
groups covering directory/archive caches and cross-source aliases, and
clean diff whitespace checks.

common/lc_piecedata.cpp

@@ -16,13 +16,7 @@ lcPieceData::lcPieceData(bool IsLibraryPiece)
 	: mIsLibraryPiece(IsLibraryPiece)
 {
 	mZipFileType = lcZipFileType::Count;
-	mZipFileIndex = -1;
-	mFolderType = -1;
-	mFolderIndex = -1;
-	mState = lcAssetState::Unloaded;
 	SetLoadingBoundingBox();
-	mFileName[0] = 0;
-	m_strDescription[0] = 0;
 }
 
 bool lcPieceData::HasDecorationDescription(const char* Description)