fix: the macOS memory test compared kilobytes against a byte floor

`memory_totals_are_internally_consistent` asserted `ram.total >= 1 GiB`
with the constant written in bytes, but `read_memory_stats` divides
`hw.memsize` by 1024 before storing it. The macOS runner reported a
correct 7 GiB as 7340032 KB, which read as 7 MB and failed the floor.
The reader was right and the test was wrong; the failure message even
said "bytes" while printing a KB figure.

`examples/cpu_monitor.rs` had a second, quieter version of the same
class of mistake: it bound `monitor` under three separate `cfg`s and
then used it unconditionally, so on macOS without the `apple` feature
no arm matched and the example did not compile. The `return` in the
fallback block does not help -- the code after it is still type-checked.
CI never saw it because the only macOS job builds `--all-features`.
The body now lives in a `report` function each platform arm calls.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>