telemetry: Move telemetry worker to its own thread

This reverts recent(ish) changes to telemetry which moved it from its own thread
onto the main thread.

The downside is: we have an extra thread.

The upside is largely that Network.zig becomes drastically simpler and more
efficient. There's a bunch of machinery in Network.zig to support arbitrary
workers, of which Telemetry is the only one. There's also a lot of code to
support an optional multi and requests made to is. This is all removed.

Also, fetch, agent and mcp without a cdp server no longer even need to start
the network loop. And, it IS started (e.g. serve/cdp), there's no longer an
arbitrary 250ms wakeup on poll to progress workers. Nor can telemtry block CDP.

Telemetry's implementation itself was changed. The ring buffer was removed in
favor of a double-buffer arraylist. When telemetry is disabled, this saves
64Kb of memory. When it's enabled, it creates more allocator churn, but should
still use less memory in most cases (and never more). Finally, Telemetry is
given its own easy connection rather than using one out of the pool (which
workers would maybe like to use).

src/network/http.zig

@@ -668,6 +668,14 @@ pub const Connection = struct {
         return self.getResponseCode();
     }
 
+    // Synchronous transfer that adds no request headers. request() injects the
+    // browser User-Agent / sec-ch-ua machinery meant for page fetches; callers
+    // that manage their own connection (telemetry) use this leaner path.
+    pub fn perform(self: *const Connection) !u16 {
+        try libcurl.curl_easy_perform(self._easy);
+        return self.getResponseCode();
+    }
+
     pub fn wsStartFrame(self: *const Connection, frame_type: libcurl.WsFrameType, size: usize) !void {
         try libcurl.curl_ws_start_frame(self._easy, frame_type, @intCast(size));
     }