Limit the probe calls at once and sort by start

Limit the probe calls at once and sort by start

onechat probe takes an optional BUILDS argument from 1 to 8, which
limits the builds that call the model at once in that run. A summarizer
with that many slots wraps the compactor, so maxBuilds in the core stays
8. A lower limit lowers the rate of calls on one cache key, which tests
whether the rate is the cause of the low cached share. The report adds
the calls per minute.

The probe reads the usage records in the order of the start of their
calls. The file holds them in the order of their end, so with calls at
once the quota stop compared the first record written with the last one,
not the earliest call with the latest, and the report showed the same
records as the first and the last call.

Issue: b14d537