b718c65267c607f8086ddb4b0f51e254a3491c87  [JSC] Using single-transition entry as a cache for the next identifier in JSON.parse

Classified as not security-relevant.
Triage note: LiteralParser gains a SIMD tryConsumeStringEqualTo / consumeColon fast path to match the next property name against an existing single structure transition, with putDirectWithoutBarrier+setStructureIDDirectly. New performance optimization (guarded by matching asserts), not a fix for an identified bug.
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: bounds_guard (+2.0), null_guard (+2.59), area:Source/JavaScriptCore/runtime (+2.5)