node:v8: diagnostics and serialization parity cut

[andrewtdiz]

Summary

Use this issue as the first public node:v8 compatibility cut focused on package-visible diagnostics and serialization. The intended PR exposes the namespace, diagnostic heap-stat shapes, top-level serialize/deserialize round trips, and the class-based Serializer/Deserializer API without trying to implement lifecycle hooks, heap snapshot output, or profiler reports.

Child Issues

• node:v8: expose serialize and deserialize round trips #3137 - expose v8.serialize() / v8.deserialize() round trips
• node:v8: expose heap statistics shape #3138 - expose heap/version diagnostic stat shapes
• node:v8: expose Serializer and Deserializer class APIs #3294 - expose Serializer and Deserializer class APIs

Follow-up Cuts

• node:v8: lifecycle callback namespaces parity cut #3295 - lifecycle callback namespaces parity cut
• node:v8: snapshot and profiler output parity cut #3296 - snapshot and profiler output parity cut

Intended PR Boundary

Implement one coherent node:v8 first slice:

• add the public node:v8 namespace and manifest/runtime dispatch for the child issues;
• expose serialization/deserialization round trips for representative Node-supported values;
• expose the class-based Serializer/Deserializer and default subclasses for the same wire-format path;
• expose heap-stat helper shapes with Perry-specific numeric data where V8 internals are unavailable;
• add a dedicated V8 parity fixture because this checkout currently has no runnable node:v8 probe.

Node Behavior

Node's node:v8 module gives packages serialization helpers and diagnostic heap/version statistics. Many packages use this surface for feature detection, persistence/IPC, and diagnostics even when they do not use profiling, promise hook, or startup snapshot APIs.

Perry Behavior

Perry currently has no public node:v8 compatibility namespace. docs/runtime-parity-gaps.md lists the whole module as a gap, docs/runtime-parity.md enumerates missing/partial rows, source search found no public node:v8 manifest/runtime entries, and there is no V8 parity fixture in this checkout. The internal crates/perry-runtime/src/child_process/v8_serde.rs helper may be reusable for the serialization child issues.

Non-goals

• v8.promiseHooks and v8.startupSnapshot APIs; use node:v8: lifecycle callback namespaces parity cut #3295.
• Heap snapshot output, GCProfiler, CPU profiling, and heap profiling surfaces; use node:v8: snapshot and profiler output parity cut #3296 or separate focused leaves.
• Exact V8 heap accounting; Perry-specific numeric diagnostics are acceptable if the Node-observable shape is compatible.

Acceptance

• Child issues node:v8: expose serialize and deserialize round trips #3137, node:v8: expose heap statistics shape #3138, and node:v8: expose Serializer and Deserializer class APIs #3294 have focused parity/regression coverage.
• A new V8 parity fixture proves the first-slice API shapes, representative serialization round trips, and Serializer/Deserializer class behavior.
• Docs/gap metadata stop presenting the covered rows as fully missing.
• Deferred promise-hook, startup-snapshot, snapshot-output, and profiler APIs remain tracked separately instead of hidden by this cut.

[proggeramlug]

Closing this "parity cut" umbrella tracker as superseded by its granular child issues.

Perry tracks Node/TypeScript parity gaps as granular, per-gap issues (the ones listed under Child Issues above) — that is the workable backlog the maintainer prefers, rather than umbrella roll-ups. Each child issue carries its own Node-vs-Perry evidence, source pointers, and test surface, and remains open and independently tracked; closing this umbrella loses no work, only the duplicate roll-up framing.

The child issues continue to be addressed by focused PRs (each PR auto-closes the specific leaf issues it fixes). If a consolidated tracker is still wanted for this module, feel free to reopen.