fix: #850 — EventEmitter listener table + static helpers match Node semantics

[proggeramlug]

Summary

EventEmitter's listener storage was a flat HashMap<String, Vec<i64>> with only on / emit / removeListener / removeAllListeners / listenerCount wired. Every other method silently no-op'd or returned undefined, and the module-level helpers didn't exist at all. EventEmitter is the base for net, http, stream, child_process and most npm packages, so the gap was foundational.

This rewrites the listener storage in both copies (perry-ext-events — active via the well-known flip when node:events is imported — and the perry-stdlib fallback) around an ordered Vec<Listener { callback, once }> per event with a parallel event_order shadow that preserves insertion order for eventNames(). emit snapshots before dispatch, prunes once-listeners from the live vec mid-emit, and drains pending events.once(em, name) promises with a single-element [arg] array.

events.once allocates a Promise per call, stashes the raw pointer in the emitter's pending_once_promises, and resolves it synchronously through perry-runtime's js_promise_resolve on the next matching emit — bypassing JsPromise::resolve_*, which routes through async_bridge::queue_promise_resolution and needs the perry-stdlib pump registered first (a coupling that doesn't hold for a pure EventEmitter program).

Wired all new methods through NATIVE_MODULE_TABLE, runtime_decls.rs declarations, and the API manifest. GC root scanner now marks both listener closures and pending Promise pointers.

Probe results (issue baseline diff = 26 → now 10)

Probe	Node	Perry before	Perry after
em.listenerCount('inc') after 2 .on()	2	0	2
em.eventNames()	[ 'inc' ]	0	[ 'inc' ]
em.once handler arg captured	[ 7 ]	[]	[ 7 ]
em.addListener / removeListener	[ 1 ]	[]	[ 1 ]
em.prependListener order	[ 'a', 'b' ]	[ 'b' ]	[ 'a', 'b' ]
em.prependOnceListener order	[ 'a', 'b', 'b' ]	[ 'b', 'b' ]	[ 'a', 'b', 'b' ]
em.listeners('inc') count	2	undefined	2
em.rawListeners('inc') count	2	undefined	2
em.getMaxListeners() after setMaxListeners(42)	42	0	42
em.removeAllListeners() then names	[]	0	[]
events.once(em,'x') module-level	resolves to array	throws Cannot read properties of undefined (reading 'length')	resolves
events.getEventListeners(em,'e')	array	throws	array

Remaining gaps (out of scope, all listed in the issue as follow-ups)

• events.on(em,'evt') async-iterator (returns [] today)
• Multi-arg emit(name, a, b) — would let events.once resolve to a 2-element array instead of 1
• newListener / removeListener meta-events
• Module-level constants: defaultMaxListeners, errorMonitor, captureRejections, captureRejectionSymbol
• events.addAbortListener

Test plan

• test-files/test_issue_850_eventemitter.ts (the probe set from the issue) — 12/13 lines match Node byte-for-byte
• test-files/test_parity_events.ts — diff dropped from baseline 26 lines → 10 lines (60% reduction)
• cargo test --release --workspace --exclude perry-ui-{ios,tvos,watchos,visionos,android,windows,gtk4} — all pass
• cargo test --release -p perry-ext-events — 6/6 doctests pass (including new prepend_listener_inserts_at_front and max_listeners_round_trips)
• test-files/test_net_min.ts — Socket .on() / .emit() still fire correctly (EventEmitter is the base class)
• cargo fmt --all
• manifest consistency test — every new dispatch entry has a matching entries.rs row

Closes #850.