Eviction processor no longer keeps cache instance alive

[majocha]

Description

Make the background eviction agent shared and do not capture references to cache instances indefinitely. Cache instances no longer manage its lifetime, they simply post work items.
Get rid of cache disposal and finalizer. Idle caches should be quickly garbage collected now.

Fixes #20756

Checklist

• Test cases added
• Performance benchmarks added in case of performance changes
• Release notes entry updated

[github-actions]

❗ Release notes required

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[T-Gro]

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