This commit implements basic NVS support for the esp32. It follows the
pattern of the esp32.Partition class and exposes an NVS object per NVS
namespace. The initial support provided is only for signed 32-bit integers
and binary blobs. It's easy (albeit a bit tedious) to add support for
more types.
See discussions in: #4436, #4707, #6780
Thorsten von Eicken