Add hash.Clone interface for HMAC and Hash

[mertakman]

This PR implements upcoming hash.Clone interface on HMAC and hashes for keeping hash.Hash returns compatible with Go 1.25.

[Copilot]

Pull Request Overview

This PR introduces a new HashCloner interface for both pre- and post-Go 1.25 environments and implements Clone on hashX so that CNG-backed hash instances remain compatible with the upcoming hash.Cloner in Go 1.25.

• Add Go 1.25–specific alias to hash.Cloner under a build tag
• Define a custom HashCloner interface (pre-1.25) and update hashX.Clone to match
• Add TestHash_Clone and a helper to validate the new clone behavior

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
cng/hashclone_go125.go	Introduce HashCloner alias to hash.Cloner for Go 1.25+ builds
cng/hashclone.go	Define custom HashCloner interface with Clone() (HashCloner, error)
cng/hash.go	Update hashX.Clone signature and type assertion to use HashCloner
cng/hash_test.go	Add TestHash_Clone and writeToHash helper to exercise clone logic

Comments suppressed due to low confidence (1)

cng/hashclone_go125.go:13

• [nitpick] Add a doc comment above this alias to explain that it bridges to the new hash.Cloner interface in Go 1.25, so readers immediately understand the purpose of this type alias.

type HashCloner = hash.Cloner

[qmuntal]

LGTM minus one comment!