Improve CPU metrics calculations for CgroupV2 - #6289

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I understand this is still in Draft state, but just a note - we will need to some Acceptance tests, similar to already existing one, where we emulate filesystem and test the library as a whole

Can we please have a test similar to this (of course we don't have to compare values with Tracker). The test will validate that the new logic picks up changes from file system as expected

Added

/backport to release/9.4

Started backporting to release/9.4: https://github.com/dotnet/extensions/actions/runs/14520112091