[EventLog] Use performance.now() rather than Date.now() to calculate elapsed time in tests

[ersin-erdal]

Resolves: #156061

Since all the failed CI results show actual elapsed time as 19 rather than 20 (expected), the issue seems like an inaccurate time calculation caused by Date.now() method.

Replacing Date.now() with the more precise performance.now() method may solve the problem.

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: d5b9b53

Failed CI Steps

• FTR Configs #37

Test Failures

• [job] [logs] FTR Configs #37 / aiops change point detection shows multiple results when split field is selected

Metrics [docs]

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	19	21	+2
securitySolution	416	420	+4
total			+6

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	20	22	+2
securitySolution	500	504	+4
total			+6

History

• 💛 Build #131294 was flaky 7445556

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @ersin-erdal

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)

[ymao1]

LGTM