Fix flaky test_race_concurrent_measurements on Windows CI (#5130)

* Initial plan

* Fix flaky test_race_concurrent_measurements on Windows CI

- Correct mock_view_matching call: pass "view1" as name argument
- Replace brittle constructor-count assertion with state-based check
  on _instrument_view_instrument_matches to avoid Windows scheduling flakiness

Assisted-by: Claude Opus 4.6

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Co-authored-by: xrmx <12932+xrmx@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: xrmx <12932+xrmx@users.noreply.github.com>