fix(cdp): emit Network events for script-initiated requests (#415)

Requests made by page JS (fetch/XHR/dynamic script and stylesheet loads)
run in the V8 op layer and never produced a NetworkEvent, so CDP emitted
Network.requestWillBeSent / responseReceived only for the static
navigation subresources. Puppeteer/Playwright page.on('request') and
on('response') therefore missed every XHR/JSON response, which breaks
response capture (and is the root cause of the Aviasales half of #394).

op_fetch_url now records a JsNetworkEvent keyed by the same fetch-{N} id
under which it already stores the response body. The Page drains these
into its network_events before the CDP layer emits, so they flow through
emit_navigation_events as requestWillBeSent / responseReceived /
loadingFinished alongside the document subresources, and
Network.getResponseBody resolves for them via the shared id. Applied to
both navigation paths (server process_navigation and in-process
do_navigate). The queue is capped at 4096 events per page.

Closes #406.

crates/obscura-js/src/runtime.rs

@@ -988,6 +988,13 @@ impl ObscuraJsRuntime {
         self.state.borrow().fetched_urls.clone()
     }
 
+    /// Drain the network events recorded for script-initiated requests
+    /// (fetch/XHR/dynamic resource). The Page moves these into its own
+    /// network_events so the CDP layer emits Network events for them (#406).
+    pub fn take_js_network_events(&self) -> Vec<crate::ops::JsNetworkEvent> {
+        std::mem::take(&mut self.state.borrow_mut().js_network_events)
+    }
+
     pub fn dom_ref(&self) -> Option<std::cell::Ref<'_, Option<DomTree>>> {
         let r = self.state.borrow();
         if r.dom.is_some() {