[MS56.1] Add NetworkStatsHistory#Builder

NetworkStatsHistory will need to be exposed and constructed
from the data migration tool in the follow-up changes.
Add a Builder class to prevent from exposing internal array
structures.

Test: atest NetworkStatsHistoryTest#testBuilder
Bug: 204830222
Change-Id: I5f8ea1c825d601de0aac8623034ef896999fc1a0