walredo benchmark: throughput-oriented rewrite

[problame]

See the updated bench_walredo.rs module comment.

tl;dr: we measure avg latency of single redo operations issues against a single redo manager from N tokio tasks.

part of #6628

[github-actions]

2706 tests run: 2573 passed, 0 failed, 133 skipped (full report)

---

Flaky tests (1)

Postgres 15

• test_sharding_split_smoke: debug

Code coverage* (full report)

• functions: 28.2% (7207 of 25519 functions)
• lines: 46.9% (44237 of 94370 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
b2f5b84 at 2024-03-21T13:49:06.654Z :recycle:}