Large file - fileshare performance

[BC89]

Using latest fileshare library preview (19) but same with lts. Performance of .startcopy is God awful on large files.

Using .net 8 and copying from blob to file share, same storage container with large files enabled. Linux container app aervice deployed in same useast region, largest consumption app 2/4 available.

Interestingly the file size looks good when observed in storage explorer but status == pending on async property callback for over a minute when about 500+ MG or so, and degrades expotentially as the siize increases.