Impl. puller for BYTES_TRANSFER_BY_TAG_AND_METERED

+ refactor puller implementation for NetworkStats pullers in order to
support arbitrary slicing of NetworkStats data

Test: adb shell cmd stats pull-source 10000~10003
Test: adb shell cmd stats pull-source 10083
Test: atest CtsStatsdHostTestCases
Bug: 144771940
Change-Id: I92809f9f8d5d14742e8ba323eb8c7792dadb802f