ci(asan): suppress Node-internal contextify singletons

Node's lazy initialisation of the global fetch() (undici) and the ESM
loader compiling web/client.js each allocate a ContextifyContext /
ContextifyScript that lives for the lifetime of the process. They are
not owned by rclnodejs, are allocated exactly once, and are reported
by LeakSanitizer at process exit only because Node does not tear down
its own VM bookkeeping.

Suppress both signatures in suppr.txt. Verified locally that the ASan
run for test-web-http.js + test-web-ws.js now exits cleanly with the
suppression counts matching the previously-unsuppressed leaks.

Author: minggangw

suppr.txt

@@ -2,4 +2,10 @@ leak:librcl.so$
 leak:ref-napi/prebuilds/linux-x64/node.napi.node$
 leak:^napi_module_register$
 leak:^napi_create_reference$
-leak:^napi_create_external$
+leak:^napi_create_external$
+# Node-internal one-shot singletons retained for the lifetime of the process.
+# Triggered by Node's lazy initialisation of the global `fetch()` (undici) and
+# the ESM loader compiling our `web/client.js` module — both allocated once,
+# never freed before process exit, and not owned by rclnodejs code.
+leak:node::contextify::ContextifyContext
+leak:node::contextify::ContextifyScript