feat(node:process): expose process.features capability flags (#2588)

[proggeramlug]

Summary

Closes the test-side gap in process.features: it is now exercised as a real, non-null object of capability flags whose chained reads (process.features.tls, process.features.typescript, etc.) work and match Node's JS types.

While investigating #2588 I found that the process.features runtime/lowering already landed in #1474 — process_features_literal() in crates/perry-hir/src/lower/expr_member.rs returns a real Expr::Object of boolean capability flags plus a typescript string. The remaining gap called out by the issue was purely on the test side: test-files/test_parity_process.ts still skipped all chained process.features.* reads with a stale "chained on undefined features crashes" comment, and there was no dedicated gap test.

This PR closes that gap:

• test-files/test_parity_process.ts — un-skips the chained feature reads. It now asserts typeof process.features, non-null-ness, and the JS type of each documented flag (boolean for the capability flags, string for typescript).
• test-files/test_gap_process_features.ts (new) — a focused gap test asserting the same deterministic structural invariants (object-ness, non-null, each key's JS type, chained read doesn't crash).

Both assert types and presence, not concrete boolean/string values, because some flags legitimately differ between a Perry build and a Node build (Perry surfaces typescript: "transform" for its AOT pipeline vs Node's "strip"; the uv / inspector / require_module booleans also differ).

Validation

Compiled with the cargo-built runtime/stdlib and compared byte-for-byte against node --experimental-strip-types.

test-files/test_gap_process_features.ts — byte-identical to Node:

typeof: object
non-null: true
inspector is boolean: true
debug is boolean: true
ipv6 is boolean: true
tls is boolean: true
tls_alpn is boolean: true
tls_ocsp is boolean: true
tls_sni is boolean: true
uv is boolean: true
cached_builtins is boolean: true
require_module is boolean: true
typescript is string: true
chained tls ok: true

test-files/test_parity_process.ts — the process.features section is byte-identical to Node (diff <(grep features node) <(grep features perry) => FEATURES_IDENTICAL), and the full fixture diff against Node is empty. Verified against the unmodified origin/main fixture as a baseline, so this PR introduces no new diffs.

• cargo fmt --all -- --check passes (no Rust files changed).
• No api-manifest entry added; process.features is handled by HIR lowering (mirroring process.report), so api-docs-drift is unaffected.

Closes #2588.