fix: fix issue introduced in #363 (#364)
fix: fix issue introduced in #363 (#364)

PR #363 added metrics descriptions, but mistakenly iterates through
the counters twice for prometheus/opentelemetry format and
incorrectly reports each counter as both a counter and a gauge.

Fixes a bad copy-paste from that PR.
brayniac/rpc-perf,twitter/rpc-perf