fix: reset cost to zero on DeleteAll

[MFactor1]

Closes #221.

When run with the reproduction shown in #221, it results in the correct output:

Cache starting size: 0
Inserting: key1
Inserting: key2
Inserting: key3
Cache size after insertion: 3
Evicting: key3
Evicting: key1
Evicting: key2
Cache size after deletion: 0
Inserting: key4
Cache size after inserting again: 1

[swithek]

Thanks for the PR. If you can, update the tests and I'll merge this.

[coveralls]

Coverage Report for CI Build 34653981857

Warning

Build has drifted: This PR's base is out of sync with its target branch, so coverage data may include unrelated changes.
Quick fix: rebase this PR. Learn more →

Coverage increased (+0.002%) to 99.743%

Details

• Coverage increased (+0.002%) from the base build.
• Patch coverage: 4 of 4 lines across 1 file are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	777
Covered Lines:	775
Line Coverage:	99.74%
Coverage Strength:	25.63 hits per line

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💛 - Coveralls

[swithek]

Well done, thanks for the changes 🫡