Make WeaverLiveCheck tolerate slow Weaver startup

[saisharan0103]

Fixes #5176.

WeaverLiveCheck was using a fixed urllib3 Retry budget while waiting for the Weaver admin /health endpoint. On slower PyPy jobs, the admin listener can still be starting when those retries are exhausted, producing repeated localhost connection-refused warnings and failing the test even when the Weaver subprocess has not failed.

This change adds a configurable startup timeout and replaces the Retry-based health probe with an explicit monotonic-deadline polling loop using short per-request timeouts. The helper still checks whether the Weaver subprocess has exited so real startup failures raise RuntimeError quickly with logs, while slow successful startups can continue until the deadline.

Focused tests cover delayed readiness succeeding and exited subprocesses still raising RuntimeError by mocking the health request and process poll paths.

ruff check tests/opentelemetry-test-utils/src/opentelemetry/test/weaver_live_check.py tests/opentelemetry-test-utils/tests/test_weaver_live_check.py reports no new findings on the changed files.
Ran pytest -x locally with no new failures.

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