Move LRU sequence to ProcessStateRecord

Move the `mLruSeq` field and its accessor methods from `ProcessRecord`
to `ProcessStateRecord`. This is a pure refactor that enhances
encapsulation and reduces `ProcessRecord`'s direct dependency on
LRU cycle details.

Bug: 425766486
Test: atest MockingOomAdjusterTests
Flag: EXEMPT pure refactor
Change-Id: Idb583186733820b8c64f2116a6129f5dd3d1731b