Right we are using the temp package for creating temp files to cache shared strings in the workbook reader. The problem is that the temp uses a global cache to keep track of its files, which is not safe for concurrent operation. In particular, the cleanup of one task will delete all files tracked globally, incl. those still needed by another task. This results in a node error that a file was not found.

In this PR we replace the temp to tmp which is safe for concurrent operations.