[#95] Implement cache purging (admin + non-admin) with timing + logging

[vpstackhub]

Summary

This PR implements the cache purge feature requested in Issue #95, providing both:

Admin-level purge via EmptyStandbyList.exe

Fallback non-admin purge (PowerShell write-flush trick)

Detailed timing logs for James to review the UX impact

Clear console debug messages to distinguish pathways

No GUI changes yet. Waiting for James' preference on how to present timing (progress bar, spinner, modal, etc.)

Test Results

TEST A -- Running inside NetBeans (non-admin)

BenchmarkWorker: ENTERING CACHE PURGE SECTION
endTime=.... (~50ms)
startTime=.... (~30ms)

**TEST B **--Running packaged build with Administrator privileges

BenchmarkWorker: ADMIN purge path selected
BenchmarkWorker: Calling UtilOs.dropOsCache()
DROP CACHE CALLED inside UtilOs
dropOsCache() returned = true
Total purge time ~1.0s

Both test paths behaved exactly as designed.

Consideration-
Based on the timing results above (~1 second for admin purge, ~80ms for fallback),
I'd love your recommendation for the GUI implementation:

1.simple toast message?

2.small modal?

3.mini-progress bar?

4.indeterminate spinner?

Happy to adjust based on your preference.