fix(https): certless createServer() listens; _http_server.kConnectionsCheckingInterval (#4974)

[proggeramlug]

Fixes #4974.

Root cause

test-https-server-async-dispose calls https.createServer() with no options at all — no key, no cert. Node constructs such a server and listen() succeeds (the missing credentials only surface per-connection, as a TLS alert during the handshake). Perry stored tls_config: None and listen() bailed with [node:https] tls config unavailable; refusing to listen before queueing the deferred 'listening' emit — so the listen callback never fired and the test hung. Async-dispose was a red herring; the options were never "torn down", they were never there.

The test additionally asserts server[kConnectionsCheckingInterval]._destroyed via require('_http_server'), which Perry didn't export.

Fix

• tls.rs: new build_certless_server_config() — a rustls ServerConfig with an always-None cert resolver. The server binds, listens, and accepts TCP; each TLS handshake aborts with a fatal alert (Node-equivalent failure mode).
• https_server.rs: the no-PEM-material path (has_pem_material() == false) now registers the certless config instead of tls_config: None. Supplied-but-unparseable key/cert keeps the existing refuse-to-listen behavior.
• kConnectionsCheckingInterval: exported from the http module arm (_http_server aliases to http in cjs_wrap) as a sentinel string key, plus an api-manifest entry so the static property read isn't compile-time-lowered to undefined. server[k] resolves through the ext-http server handle dispatch to a minimal { _destroyed } Timeout shape; the flag lives on HttpServer and is set by all three close paths (http / https / http2).
• Docs (perry.d.ts, reference.md) regenerated via scripts/regen_api_docs.sh.

Verification

All compiled with this branch's perry + auto-optimized ext crates, against the Node v22 corpus tests staged with the test-compat/node-core/shim common:

test	before	after
test-https-server-async-dispose	hang (timeout), "tls config unavailable"	exit 0, all mustCalls fire
test-http-server-async-dispose	—	exit 0
test-http2-server-async-dispose	—	exit 0
with-key/cert https server + https.get round-trip (regression)	—	body: ok, exit 0

Behavior cross-checked against node v26 (certless server listens, disposes, _destroyed === true).

cargo test -p perry-ext-http-server -p perry-api-manifest green (23 + 36), cargo fmt --check clean, file-size gate OK.

No version bump / changelog — maintainer folds metadata at merge.