Inference Plugin: Adds status trigger based on route krt collection

[danehans]

Description

Motivation

E2E tests were flaky when an HTTPRoute and its referenced InferencePool were created in the same manifest.
If the HTTPRoute reconciled before the InferencePool, the pool never received Accepted/ResolvedRefs status conditions, preventing the route from becoming Accepted=True.

What Changed

• Bidirectional reconciliation
  • Added a krt.Index that maps Route -> InferencePool so the plugin can look up all routes that reference a pool.
  • Registered a watcher on the HTTPRoute collection to re-enqueue (reconcile) the affected pool whenever any route is added, updated, or deleted.
• Early status calculation
  • The callback runs even when the Routes collection is not yet initialized, allowing Accepted/ResolvedRefs status conditions to be set at start-up.
• Changed code
  • endpointpicker/status.go: new reverse index and updated event handling.
  • krtcollections/policy.go: exposed HTTPRoutes() and lightweight Lookup() helper.
  • No change to public API; behaviour is internal to the Endpoint-Picker plugin.

Related issues

Fixes #11516
Fixes #11379

Change Type

/kind bug_fix  
/kind flake

Changelog

Inference EndpointPicker (EPP) plugin now recalculates InferencePool status whenever an HTTPRoute that references the pool is added, updated, or deleted.

Additional Notes

[danehans]

xref #11503