Adds counts of idle and wait records to basic_counts, which are useful
when examining core-sharded-on-disk traces.

Rewords "scheduling markers" to "timestamp + cpuid markers" to clarify.
Rewords "transfer markers" to "kernel transfer markers".

Updates the tests; the core-serial tests non-zero output here, and the
core-sharded test also manually tested non-zero output as it required
removing these counts for reliable comparison of record vs replay.

Issue: #6685