Simplify flavorassigner to only return bool if borrowing is required

[mimowo]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

To make the logic simpler, and easier to modify in #1397.

Which issue(s) this PR fixes:

Part of #1337

Special notes for your reviewer:

The only exported API where we use assignment.TotalBorrow is Borrows() used by scheduler:

func (a *Assignment) Borrows() bool {
	return len(a.TotalBorrow) > 0
}

So, it is much simpler to just keep a bool "borrowing" instead, it will also have better memory usage.

Does this PR introduce a user-facing change?

NONE

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[mimowo]

/assign @yaroslava-serdiuk

[yaroslava-serdiuk]

Nice 👍
/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: e57d0128dd4ffaf46ab85b487cc0473c54dca7ab

[mimowo]

/assign @alculquicondor @tenzen-y

[tenzen-y]

As I can see the commit history, the TotalBorrow looks like there have been no changes since we implemented flavorAssigner: #454

Also, the scheduler's borrowing implementation based on flavorAssigner looks like there have been no changes since we implemented the kueue 2 years ago:

kueue/pkg/scheduler/scheduler.go

Lines 74 to 76 in 8467cdc

	// borrows is the resouces that the workload would need to borrow from the
	// cohort if it was scheduled in the capacity.
	borrows capacity.Resources

Furthermore, we have been using TotalBorrow only to confirm if the podSet borrows resources from others. In other words, we have never used stored borrowed resources in TotalBorrow anywhere since we implemented the kueue scheduler.

So, I think that this simplification would be better since we can reduce unneeded calculation costs and avoid no need complications.
cc: @alculquicondor

/lgtm
/approve

[k8s-ci-robot]

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[alculquicondor]

The information could have been useful for debugging, but otherwise not necessary in production.