Fix ExtractItems duplication with WithAppendKeyFields

[mrIncompetent]

What

Fixes ExtractItems duplicating atomic elements when extracting from associative lists with WithAppendKeyFields.

Why

Items with elementRelationship: atomic were processed twice - once for direct path match and again during sub-path checking, causing duplication in the output.

Example

When extracting with fieldpaths:

• .metadata.labels["app"]
• .metadata.labels["version"]
• .metadata.labels["env"]
• .metadata.ownerReferences[uid="123e4567-e89b-12d3-a456-426614174000"]

Before fix - ownerReference was duplicated:

{
  "metadata": {
    "labels": {
      "app": "my-app",
      "version": "v1.0.0",
      "env": "prod"
    },
    "ownerReferences": [
      {
        "apiVersion": "apps/v1",
        "blockOwnerDeletion": true,
        "controller": true,
        "kind": "Deployment", 
        "name": "my-deployment",
        "uid": "123e4567-e89b-12d3-a456-426614174000"
      },
      {
        "apiVersion": "apps/v1",
        "blockOwnerDeletion": true,
        "controller": true,
        "kind": "Deployment",
        "name": "my-deployment",
        "uid": "123e4567-e89b-12d3-a456-426614174000"
      }
    ]
  }
}

After fix - ownerReference appears only once:

{
  "metadata": {
    "labels": {
      "app": "my-app",
      "version": "v1.0.0",
      "env": "prod"
    },
    "ownerReferences": [
      {
        "apiVersion": "apps/v1",
        "blockOwnerDeletion": true,
        "controller": true,
        "kind": "Deployment",
        "name": "my-deployment",
        "uid": "123e4567-e89b-12d3-a456-426614174000"
      }
    ]
  }
}

[k8s-ci-robot]

Hi @mrIncompetent. Thanks for your PR.

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[alvaroaleman]

/ok-to-test

[mrIncompetent]

Ping @jpbetz and @liggitt

[jpbetz]

One readability suggestion then LGTM

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jpbetz, mrIncompetent

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[mrIncompetent]

Squashed the commits, did an additional renaming to improve readability.

[mrIncompetent]

Ping @jpbetz

[mrIncompetent]

Ping @jpbetz

[jpbetz]

/lgtm