Function parse_mode 

pub fn parse_mode(raw: Option<&str>) -> PlannerMode

Pure parser for the SVOD_MEMORY_PLANNER env var, exposed for testing.

Default (env unset) is PlannerMode::Arena, matching tinygrad’s NO_MEMORY_PLANNER=0 default — the arena planner runs unless the user explicitly opts out. remap / pool keep the older liveness-based pool reuse for parity with the previous default if a workload regresses.