Don't consider archived timelines for synthetic size calculation

[arpad-m]

Archived timelines should not count towards synthetic size.

Closes #9384.

Part of #8088.

[github-actions]

5290 tests run: 5075 passed, 1 failed, 214 skipped (full report)

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Failures on Postgres 17

• test_sharding_split_failures[failure4]: debug-x86-64

# Run all failed tests locally:
scripts/pytest -vv -n $(nproc) -k "test_sharding_split_failures[debug-pg17-failure4]"

Flaky tests (2)

Postgres 17

• test_local_only_layers_after_crash: debug-x86-64
• test_readonly_node_gc: debug-x86-64

Code coverage* (full report)

• functions: 31.4% (7663 of 24424 functions)
• lines: 48.8% (60268 of 123400 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
c94a437 at 2024-10-26T13:37:09.311Z :recycle:}