Performance: Tiotest: use lib_performance numeric helpers and reduce unknown fields

Update Tiotest runner to rely on shared lib_performance helpers.

- Switch to norm_metric()/is_number()/append_if_number() from lib_performance.sh
- Avoid printing misleading 'unknown' when latency fields are intentionally hidden
- Keep baseline gating, iteration flow, and output format unchanged otherwise

Signed-off-by: Srikanth Muppandam <smuppand@qti.qualcomm.com>

Author: smuppand