fix(fastify): non-blocking listen() + main-thread pump

[proggeramlug]

Summary

Closes the in-process fastify timeout from the compat sweep. /tmp/perry-compat-sweep/fastify/entry.ts was hanging at Server listening on http://0.0.0.0:18932 until gtimeout 30s killed it (rc=124). Now exits cleanly with ok=true.

Root cause

js_fastify_listen (in BOTH perry-stdlib's bundled adapter crates/perry-stdlib/src/fastify/server.rs AND perry-ext-fastify crates/perry-ext-fastify/src/server.rs) entered a blocking inner event_loop(...) that never returned, so:

await app.listen({ port: 18932 });   // never resumed
const r = await fetch("http://127.0.0.1:18932/ping");  // unreachable
const j = await r.json();             // unreachable
console.log("ok=" + j.ok);            // unreachable
await app.close();                    // unreachable

This is the same shape of bug that #604 fixed for node:http in perry-ext-http-server. Apply that pattern to fastify.

Fix

• listen() returns immediately after spawning the accept loop.
• Per-server mpsc receiver moved from the event_loop stack into FastifyServerHandle (Mutex<Option<...>>) so the main pump can find it.
• New js_fastify_process_pending drains pending requests from every registered handle each tick. Wired into perry-stdlib's js_stdlib_process_pending.
• New js_fastify_has_active keeps the runtime's main event loop alive while any server is in the "listening" state. Wired into perry-stdlib's js_stdlib_has_active_handles.
• app.close() previously fell through to "unknown native method" and silently no-op'd. Added an entry to the codegen NATIVE_MODULE_TABLE routing to a new js_fastify_app_close that walks the handle registry for matching servers, flips their listening flag, drops their rx, and fires shutdown — so the runtime exits naturally after the user calls close.
• New external-fastify-pump feature, activated by the well-known flip when bundled-fastify is stripped (import 'fastify' → perry-ext-fastify). Mirrors external-{net,ws,http-server}-pump.

Files touched

• crates/perry-stdlib/src/fastify/server.rs — non-blocking listen, new process_pending/has_active, app_close
• crates/perry-ext-fastify/src/server.rs — same shape for the external crate
• crates/perry-stdlib/Cargo.toml — new external-fastify-pump feature
• crates/perry-stdlib/src/common/async_bridge.rs — wire the new pump and has-active gate
• crates/perry-stdlib/src/common/dispatch.rs — route app.close() runtime dispatch
• crates/perry-stdlib/src/common/handle.rs — new iter_handle_ids_of helper
• crates/perry-codegen/src/lower_call.rs — new fastify close entry in NATIVE_MODULE_TABLE
• crates/perry-codegen/src/runtime_decls.rs — declare js_fastify_app_close
• crates/perry/src/commands/compile/optimized_libs.rs — activate external-fastify-pump on the flip
• test-files/test_fastify_in_process.ts — new smoke test mirroring the compat-sweep fixture

Test plan

• Compat-sweep fastify fixture now passes (rc=0, prints ok=true).
• Output matches Node: ok=true.
• scripts/run_fastify_tests.sh end-to-end suite passes (10/10 routes).
• cargo test --release -p perry-stdlib --lib fastify — 22/22 fastify unit tests pass.
• test-files/test_fastify_in_process.ts (new) compiles and runs to ok=true rc=0.

No version bump or changelog change (maintainer folds those in at merge time).