feat(compute): Add perf test for compute startup time breakdown

[ololobus]

Problem

We had a recent Postgres startup latency (start_postgres_ms) degradation, but it was only caught with SLO alerts. There was actually an existing test for the same purpose -- start_postgres_ms, but it's doing only two starts, so it's a bit noisy.

Summary of changes

Add new compute startup latency test that does 100 iterations and reports p50, p90 and p99 latencies.

Part of https://github.com/neondatabase/cloud/issues/24882

[github-actions]

7964 tests run: 7580 passed, 0 failed, 384 skipped (full report)

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Code coverage* (full report)

• functions: 32.3% (8739 of 27024 functions)
• lines: 48.4% (74891 of 154746 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
ae4948f at 2025-03-18T18:42:01.428Z :recycle:}