Make Raw Image Remount Deterministic

[jaredhagel2]

Summary

This changes the raw-image post-write remount path so Rufus consistently remounts the primary partition instead of whichever volume Windows happens to expose first.

It also makes raw-image writes reuse the earliest previously assigned drive letter for the target disk, which avoids stealing the secondary partition's mountpoint in the common multi-partition D:/E: case.

Problem

When writing a multi-partition raw image, the post-write mount state depended on the target disk's prior drive-letter state.

In the failure case, Rufus would reuse the last removed drive letter and then try to remount the primary partition onto a letter that already belonged to the secondary partition. The remount flow also looked up the volume with partition offset 0, which is ambiguous and can resolve to whichever matching volume Windows exposes first.

In the end, this caused our 2 partition USB drive to only show up as D: within Windows Explorer after imaging with Rufus, which then required the user to manually correct by assigning the letter E to the second partition using the Windows 'Disk Management' tool.

Fix

• Use the refreshed main-partition offset when waiting for and resolving the remounted logical volume.
• In raw-image mode only, reuse the first removed drive letter instead of the last removed drive letter.

This keeps the change narrow while making the remount target deterministic.

Validation

• Verified on the CFast raw-image workflow that the recurring mount-letter collision no longer reproduces.