fix(layer): metric miscalculations

[koivunej]

Split off from #7030:

• each early exit is counted as canceled init, even though it most likely was just LayerInner::keep_resident doing the no-download repair check
• downloaded_after could had been accounted for multiple times, and also when repairing to match on-disk state

Cc: #5331

[github-actions]

2682 tests run: 2560 passed, 0 failed, 122 skipped (full report)

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Code coverage* (full report)

• functions: 28.3% (7031 of 24809 functions)
• lines: 47.1% (43494 of 92433 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
b795eda at 2024-03-15T11:52:20.279Z :recycle:}