Update gcPaceScavenger function to include new scavenger behavior a…

…nd goals

* **gcPaceScavenger function:**
  - Add memory limit goal calculation and update logic
  - Add gcPercent goal calculation and update logic
  - Adjust goal alignment to physical page boundary
  - Update heapRetainedNow calculation and comparison with goals

* **scavenge struct:**
  - Add `memoryLimitGoal` and `gcPercentGoal` fields
  - Add `assistTime` and `backgroundTime` fields

* **scavengerState struct:**
  - Add `targetCPUFraction`, `sleepRatio`, and `sleepController` fields
  - Add `controllerCooldown`, `sleepStub`, `scavenge`, `shouldStop`, and `gomaxprocs` fields