Lower the footprint of the class verification fuzzer

* Remove native debug info in class fuzzer
* Reclaim arena pool memory

As a drive-by, move skipped_gc_iterations which solves
a one-off calculation.

Bug: 430216770
Flag: EXEMPT testing only
Test: Run the fuzzer until OOM, seeing the live heap allocations
Change-Id: I945f5b8920fc775ca2c24c4fbc36383489b7d632