perf: intern decayinginformer strings with unique package

[SOF3]

Description

Intern strings instead of just deep-cloning them to reduce memory usage.

• unique package uses a WeakMap, so there is no memory leak
• Only highly repetitive strings are interned. Non-event object names and resource versions rarely repeat, so they are not interned.
• unique package handles string cloning internally, so we don't need to do it again.

Related issues

Special notes for your reviewer:

[Copilot]

Pull Request Overview

This PR optimizes memory usage in the decaying informer by introducing string interning using Go's unique package. Instead of deep-cloning all strings, it selectively interns highly repetitive strings like cluster, group, resource, and namespace names while continuing to clone less repetitive strings like object names and resource versions.

• Added InternString helper function using the unique package
• Updated Key.Clone() and VersionedKey.Clone() methods to intern cluster, group, resource, and namespace fields
• Updated DecayedOf function to intern namespace and name fields

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
pkg/util/reflect/reflect.go	Added InternString utility function using unique package
pkg/util/object/key.go	Updated Clone methods to intern repetitive string fields instead of cloning
pkg/util/informer/decaying_informer.go	Updated DecayedOf to intern namespace and name fields

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