node:v8: implement GCProfiler report shape

[andrewtdiz]

Summary

new v8.GCProfiler() should expose a profiling object whose start() / stop() methods collect and return a GC profiler report. Perry currently has no public node:v8 GCProfiler implementation.

Node Behavior

A minimal Node probe shows the profiler shape:

const v8 = require("node:v8");
const profiler = new v8.GCProfiler();
console.log(typeof v8.GCProfiler, profiler.constructor.name);
console.log(typeof profiler.start, typeof profiler.stop);
console.log(profiler.start());
const result = profiler.stop();
console.log(Object.keys(result));

Observed on Node v25.9.0: GCProfiler is a constructor; instances expose function-valued start and stop; start() returns undefined; stop() returns an object with keys including version, startTime, statistics, and endTime.

Perry Behavior

docs/runtime-parity.md marks new GCProfiler() missing under node:v8. docs/runtime-parity-gaps.md tracks node:v8 as a whole-module gap, source search found no public node:v8 GCProfiler implementation, and there is no dedicated V8 parity fixture in this checkout.

Suggested PR Cut

Batch this with related issues in:
#3296 - node:v8: snapshot and profiler output parity cut

Good batch candidates:

• node:v8: implement heap snapshot output #3140

Do not batch with:

• unrelated modules
• broad subsystem rewrites
• fixes needing different test harnesses
• serialization/heap-stat diagnostics (node:v8: expose serialize and deserialize round trips #3137, node:v8: expose heap statistics shape #3138, node:v8: expose Serializer and Deserializer class APIs #3294)
• promise lifecycle hooks (node:v8: implement promiseHooks lifecycle callbacks #3139)
• startup snapshot APIs (node:v8: expose startupSnapshot helper state #3141)
• CPU profiling / heap profiling handle APIs

Acceptance

• A parity/regression test proves new v8.GCProfiler() returns an object with function-valued start and stop.
• start() returns undefined, and stop() returns an object with Node-compatible report keys for the covered case.
• The profiler data may reflect Perry internals or a minimal compatible report, but the constructor/method/report shape matches Node for package diagnostics.
• Related known-failure/docs/manifest entries are updated if touched.

[andrewtdiz]

I am taking this with #3140 as one focused node:v8 snapshot/profiler output cut. Intended PR scope: add Node-shaped GCProfiler construction, start() / stop() behavior, and minimal report keys alongside the heap snapshot stream/file output work. Non-goals: exact V8 internals, startup snapshot APIs, serialization/heap-stat diagnostics, promise lifecycle hooks, and CPU/heap profiling handle APIs.

[andrewtdiz]

Opened draft PR #4182 for this: #4182

It includes stateful GCProfiler construction, start() / stop() behavior, a minimal Node-shaped report object, and parity fixture coverage for namespace and named-import construction.