chore(test): add GpuChipTestBuilder::new_persistent

[DeVikingMark]

Add OPENVM_GPU_TEST_PERSISTENT env var support to GpuChipTestBuilder::new().

Defaults to volatile memory for backward compatibility. Set to 1 to enable persistent mode.

[jonathanpwang]

Not sure why we want this? It doesn't simplify any code

[DeVikingMark]

Fair point. After thinking it through, for a while I've refactored to add new_persistent() method instead, matching the default_persistent() pattern in VmChipTestBuilder. This is more explicit and better I suppose.