feat(stackresource): report the last port-dial result on status

[ashishmax31]

What

PortCheck used to exist only while a declared port was failing — written on the first refusal seen while serving, deleted once every port verified open. The hub had nothing to build a release event from, and no way to tell "ports verified" from "never checked".

It now reports what the last dial said, on both the serving and the not-serving path:

field	meaning
status	Success or Failure — the result of the last dial
failingPortNumbers	the declared ports that refused it
failingSince	when the grace window opened, set only while one is open

A port that is slow to bind reports Failure and then Success once it comes up. That is intended: it tells the user the ports were actually scanned, and the follow-up corrects it. The workload is still only condemned when a Failure outlives the grace window — that behaviour and the 3 minute default are unchanged.

How

failingSince keeps its old job as the operator's countdown, and only verifyServingPorts sets it. It is read through one helper:

func graceWindowStart(pc *v1alpha1.PortCheckStatus, revision string) *metav1.Time {
	if pc == nil || pc.Revision != revision {
		return nil
	}
	return pc.FailingSince
}

A Success record has no timestamp, so a port that goes bad after verifying open opens a fresh window instead of reading through a nil pointer.

capturePortDiagnosisForNotServingWorkload (renamed from capturePortDiagnosis, so the precondition is in the name) reports the dial but never opens the window. A pod that has not started listening yet must not burn it, or the serving path would condemn on its first refusal. Writing the same record on every pass also keeps StatusHash stable, so a not-serving workload no longer looks like it is changing on every reconcile.

Tests

Two new specs in readiness_failure_test.go:

• opens a fresh window when a verified-open port goes bad on the same revision — the nil-pointer path.
• reports the dial without opening the grace window, and writes the same record every pass — asserts failingSince stays nil and StatusHash() does not move across three passes.

Existing specs updated for the pointer field and for Success now writing a record instead of clearing it.

make test green.

Follow-up

Hub side: show Failure as in-progress while the resource is still Pending, and as a failed release once it is Failed/Stalled. Related to the open thread on mapping Phase=Failed + Available=True.