b4925b759d58d7263d828afc861163305f079e18  requestIdleCallback handles above 2^31 cannot be cancelled because C++ uses int for the IDL unsigned long handle

Classified as not security-relevant.
Triage note: Changes requestIdleCallback/cancelIdleCallback identifiers from int to unsigned across Document/DOMWindow/IdleCallbackController, replacing the `signedIdentifier <= 0` guard with `!identifier`. Signedness/type cleanup of opaque handles; no security impact.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+6.47), null_guard (+1.2), area:Source/WebCore/dom (+2.0), surgical (+1.3)