Add or migrate to `peakAllocated`

[Rosuavio]

It feels like It would be useful to have a more granular (or absolute) measurement of the "Peak Allocated".

It seems like we can either change peakMbAllocated to peakAllocated or add a peakAllocated along side peakMbAllocated.

For pre 4.10.0 we fill in the imprecision with zeros, and for 4.10.0 on we use the precise bytes.