chore: Refactor Vars and StringOrSlice types into adc package

[dspo]

Moved the Vars and StringOrSlice types from the common package to the adc package to better encapsulate related functionality. Updated import paths and references accordingly to reflect this change.

Type of change:

• Bugfix
• New feature provided
• Improve performance
• Backport patches
• Documentation
• Refactor
• Chore
• CI/CD or Tests

What this PR does / why we need it:

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[github-actions]

conformance test report

apiVersion: gateway.networking.k8s.io/v1
date: "2025-04-16T03:15:33Z"
gatewayAPIChannel: standard
gatewayAPIVersion: v1.2.0
implementation:
  contact: null
  organization: API7
  project: api7-ingress-controller
  url: https://github.com/api7/api7-ingress-controller.git
  version: v2.0.0
kind: ConformanceReport
mode: default
profiles:
- core:
    failedTests:
    - HTTPRoutePathMatchOrder
    - HTTPRouteServiceTypes
    result: failure
    skippedTests:
    - GatewayInvalidTLSConfiguration
    - GatewaySecretInvalidReferenceGrant
    - GatewaySecretMissingReferenceGrant
    - GatewaySecretReferenceGrantAllInNamespace
    - GatewaySecretReferenceGrantSpecific
    - HTTPRouteExactPathMatching
    - HTTPRouteHTTPSListener
    - HTTPRouteHeaderMatching
    - HTTPRouteHostnameIntersection
    - HTTPRouteInvalidBackendRefUnknownKind
    - HTTPRouteInvalidCrossNamespaceBackendRef
    - HTTPRouteInvalidCrossNamespaceParentRef
    - HTTPRouteInvalidNonExistentBackendRef
    - HTTPRouteInvalidParentRefNotMatchingSectionName
    - HTTPRouteInvalidReferenceGrant
    - HTTPRouteListenerHostnameMatching
    - HTTPRouteMatching
    - HTTPRouteMatchingAcrossRoutes
    - HTTPRoutePartiallyInvalidViaInvalidReferenceGrant
    - HTTPRouteReferenceGrant
    - HTTPRouteRequestHeaderModifier
    - HTTPRouteWeight
    statistics:
      Failed: 2
      Passed: 9
      Skipped: 22
  name: GATEWAY-HTTP
  summary: Core tests failed with 2 test failures.

[Copilot]

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

api/adc/types.go:530

• The definition of StringOrSlice has been changed so that the SliceVal field is now declared as []StringOrSlice instead of []string as in the previous implementation. This recursive type declaration could lead to unintended behavior; please confirm if this change is intentional or update it to []string if the original logic was intended.

SliceVal []StringOrSlice `json:"-"`