Expose the interception infrastructure that already existed internally but was
private, so embedders can intercept, observe, mock, or block JS fetch()/XHR
without forking or unsafe casts.
On obscura::Page:
- add_preload_script: inject JS before any page <script> (CDP
Page.addScriptToEvaluateOnNewDocument). The field already ran the scripts;
this only adds the method.
- enable_interception: returns a receiver for every JS fetch()/XHR request;
resolve each through its resolver with InterceptResolution::{Continue,
Fulfill, Fail} to pass, mock, or block (CDP Fetch.enable equivalent).
- on_request / on_response: passive callbacks. on_response is the main path for
capturing API response payloads from SPAs.
on_request/on_response previously fired only for navigation; op_fetch_url now
invokes them for JS fetch()/XHR too (both reqwest and stealth paths), gated on
a non-empty callback vector so the common no-callback case pays nothing.
Re-export InterceptedRequest, InterceptResolution, RequestInfo, ResourceType,
RequestCallback, ResponseCallback, Response from the obscura crate.
Integration test tests/interception.rs exercises all three against a local echo
server.