test: fix latency measurement in NLG

[alex-kuzmin-hg]

Description:

Related issue(s):

Fixes #25128

Notes for reviewer:

Checklist

• [ X] Documented (Code comments, README, etc.)
• [ X] Tested (unit, integration, etc.)

[lfdt-bot]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues

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[alex-kuzmin-hg]

Passed smoke SDLT: https://perf.analytics.eng.hashgraph.io/ephemeral/test_runs/main_AdHocSD8_679/report/longevity/client.log

[codacy-production]

Not up to standards ⛔

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