Emits jemalloc’s own runtime accounting (stats.allocated/resident/
mapped/retained). Only meaningful when jemalloc is this process’s
global allocator, hence the feature + platform gate.
Emits this process’s own RSS/virtual memory size. Allocator-agnostic
(reads from the OS via sysinfo), so this runs for every consumer of
spawn_system_monitor, including non-jemalloc binaries.
True once at least SLOW_SAMPLE_INTERVAL has elapsed since the last slow
sample. Extracted as a pure function (mirroring saturation_monitor.rs’s
sample_once extraction) so the gating decision itself is directly
testable with plain Duration values, rather than only reachable from
inside the infinite loop below.