Function create_isolate 

pub fn create_isolate(heap_limit_mb: Option<u32>) -> OwnedIsolate

Create a new V8 isolate with an optional heap limit in MB. None applies the bounded-by-default cap (DEFAULT_HEAP_LIMIT_MB) — an isolate is NEVER created with an unbounded heap, so a guest heap bomb terminates its own isolate rather than fatal-aborting the shared process.