fix: skip provisioning pods already claimed by healthy in-flight NodeClaims

[aardbol]

Fixes #3121

Description

Karpenter was launching duplicate NodeClaims for the same pending pods while their first NodeClaim was still in-flight (not yet registered/initialized). The pod→NodeClaim mapping existed but was only used for metrics. GetPendingPods now skips pods already claimed by a healthy in-flight NodeClaim, and releases them when that claim goes away (deleted, terminating, launch/registration timeout, or initialized), so no excess nodes are launched during the registration window.

How was this change tested?

• Added regression coverage in pkg/controllers/provisioning/suite_test.go:
  • pod claimed by a healthy in-flight NodeClaim is excluded from GetPendingPods
  • mapping/pod released on NodeClaim deletion, terminating, launch timeout, registration timeout, and initialization
  • stale mapping dropped on missing NodeClaim without resetting metric state
• End-to-end verification (with https://github.com/upcloud-tools/karpenter-provider-upcloud):
  • 1 concurrent pod → 1 NodeClaim (previously 2)
  • 3 simultaneous pods → 1 NodeClaim, all pods Running
  • no duplicate NodeClaims across multiple reconciliation loops spanning the node-registration window

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: aardbol / name: aardbol (af20081)

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