MLBEDSW-8467: verbose-allocation memory usage is incorrect

 - The issue was that the peak memory usage was only evaluated at the
start of the tensor's lifetime and not across its whole lifetime
 - The fix is to look for the maximum usage between start and end

Change-Id: Iff4f390f3a017f1df0f8933796fa5282db7870db
Signed-off-by: Tim Hall <tim.hall@arm.com>