[codex] Implement node:v8 heap snapshot and GCProfiler output

[andrewtdiz]

Summary

• Implements node:v8 heap snapshot output for getHeapSnapshot() and writeHeapSnapshot(), including readable stream/file behavior, path/options validation, and minimal heap snapshot JSON.
• Adds stateful GCProfiler construction with start() / stop() behavior and a Node-shaped report object for namespace and named-import construction.
• Updates the v8 runtime exports, native dispatch paths, parity documentation, and Node parity fixtures for the covered surfaces.

Issues

Closes #3140
Closes #3142

Why batched

Both changes cover node:v8 output/reporting surfaces and share the same runtime export, native dispatch, and parity documentation area. Landing them together keeps the v8 compatibility slice coherent while still leaving exact V8 internals out of scope.

Tests

• cargo fmt --all
• cargo fmt --all -- --check
• git diff --check
• git diff --cached --check
• ./scripts/check_file_size.sh
• RUSTC_WRAPPER= SCCACHE_DISABLE=1 CARGO_BUILD_JOBS=2 cargo check -p perry-runtime -p perry-codegen -p perry-hir
• RUSTC_WRAPPER= SCCACHE_DISABLE=1 CARGO_BUILD_JOBS=2 cargo build --release -p perry -p perry-runtime
• RUSTC_WRAPPER= SCCACHE_DISABLE=1 CARGO_BUILD_JOBS=2 cargo test -p perry-runtime readable_from_set_encoding_read_decodes_buffer_chunks
• Node/Perry comparison for test-parity/node-suite/v8/gc-profiler/report-shape.ts
• Node/Perry comparison for test-parity/node-suite/v8/heap-snapshot/output.ts
• Node/Perry comparison for test-parity/node-suite/v8/startup-snapshot/shape.ts
• Perry compile/run for test-parity/node-suite/v8/exports/diagnostics-surface.ts; local Node v22.22.1 lacks the startCpuProfile named export needed to run that fixture as a Node baseline.

Non-goals / limitations

• Heap snapshot and GCProfiler outputs are minimal compatible JSON/report shapes, not exact V8 internal dumps.
• This does not implement startup snapshot building, serializer/deserializer internals, additional heap-stat diagnostics beyond existing surfaces, promise lifecycle hooks, or CPU/heap profiling handles.