Live restore cannot handle a version downgrade if the restoration process has not yet completed. A complete restore can be determined from the stat live restore state when it is equal to WT_LIVE_RESTORE_COMPLETE 0x2.

#define WT_LIVE_RESTORE_INIT 0x0
#define WT_LIVE_RESTORE_IN_PROGRESS 0x1
#define WT_LIVE_RESTORE_COMPLETE 0x2

We should check for this when attempting a downgrade and fail the downgrade until the restoration is complete.