node:v8: expose heap statistics shape #3138

Summary

node:v8 should expose diagnostic heap/version stat helpers with Node-compatible object shapes: cachedDataVersionTag(), getHeapStatistics(), getHeapCodeStatistics(), and getHeapSpaceStatistics(). Perry currently has no public node:v8 namespace implementation for these diagnostic APIs.

Node Behavior

A minimal Node probe shows the expected diagnostic shapes:

const v8 = require("node:v8");
console.log(typeof v8.cachedDataVersionTag(), v8.cachedDataVersionTag());
console.log(Object.keys(v8.getHeapStatistics()).sort());
console.log(Object.keys(v8.getHeapCodeStatistics()).sort());
console.log(v8.getHeapSpaceStatistics()[0]);

Observed on Node v25.9.0: cachedDataVersionTag() returns a number; getHeapStatistics() returns numeric fields such as total_heap_size, used_heap_size, heap_size_limit, external_memory, number_of_native_contexts, and total_allocated_bytes; getHeapCodeStatistics() returns numeric code/bytecode/script-source/profiler fields; getHeapSpaceStatistics() returns an array of objects with space_name, space_size, space_used_size, space_available_size, and physical_space_size. Extra arguments are ignored for these helpers.

Perry Behavior

docs/runtime-parity-gaps.md lists v8.cachedDataVersionTag(), v8.getHeapCodeStatistics(), v8.getHeapSpaceStatistics(), and v8.getHeapStatistics(); docs/runtime-parity.md marks them missing. Source search across crates/perry-api-manifest/src/entries.rs, crates/perry-runtime/src, crates/perry-codegen/src, and crates/perry-stdlib/src found no public node:v8 diagnostic-stat implementation. There is no dedicated V8 parity fixture in this checkout.

Suggested PR Cut

Batch this with related issues in:
#2492 - node:v8: diagnostics and serialization parity cut

Good batch candidates:

• node:v8: expose serialize and deserialize round trips #3137
• node:v8: expose Serializer and Deserializer class APIs #3294

Do not batch with:

• unrelated modules
• broad subsystem rewrites
• fixes needing different test harnesses
• promise hook APIs
• startup snapshot APIs
• heap snapshot stream/file output
• profiler handle APIs

Acceptance

• A parity/regression test proves cachedDataVersionTag(), getHeapStatistics(), getHeapCodeStatistics(), and getHeapSpaceStatistics() return Node-compatible object/array shapes with numeric values for covered keys.
• Extra arguments are ignored for the covered helpers, matching Node.
• Values may reflect Perry internals rather than V8 internals, but field names and value types match Node for package feature detection.
• Related known-failure/docs/manifest entries are updated if touched.