Refactor estimation

[kisieland]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Introduces optimization to the binpacking estimator, which changes the time complexity from O(pods * nodes) to O(pods) in cases of homogeneous pods.

The PR also introduces a benchmark that shows 5x improvement:
The previous version took ~25s:

goos: linux
goarch: amd64
pkg: k8s.io/autoscaler/cluster-autoscaler/estimator
cpu: AMD EPYC 7B12
BenchmarkBinpackingEstimate-48    	       1	25418848308 ns/op	15018690016 B/op	144793817 allocs/op
PASS
ok  	k8s.io/autoscaler/cluster-autoscaler/estimator	25.488s

The new version takes less than 5s:

goos: linux
goarch: amd64
pkg: k8s.io/autoscaler/cluster-autoscaler/estimator
cpu: AMD EPYC 7B12
BenchmarkBinpackingEstimate-48    	       1	4805105872 ns/op	2023739088 B/op	 3574976 allocs/op
PASS
ok  	k8s.io/autoscaler/cluster-autoscaler/estimator	4.869s

Which issue(s) this PR fixes:

Special notes for your reviewer:

Split the PR into two commits:
First one introduces a required pod-equivalence abstraction
Second one uses this new fact in the estimation

For now I kept the logic in one function in the estimation to make clear what changes were made, but I am happy to split it into further functions.

Does this PR introduce a user-facing change?

No

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

NA

[k8s-ci-robot]

Hi @kisieland. Thanks for your PR.

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[kisieland]

/assign @x13n

[x13n]

/ok-to-test

[x13n]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kisieland, x13n

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