fix(browser): pause intercepted subresources instead of blocking them

[marcoripa96]

Fixes #643.

should_block_url treated Fetch interception patterns as a block list, so any <script src> or <link rel="stylesheet"> matching them was dropped before fetch and the client never asked. Puppeteer's setRequestInterception(true) enables Fetch with pattern *, so in practice every subresource of every page silently vanished the moment a puppeteer client turned interception on, whatever its request handler intended — a handler aborting only *.css* lost all scripts too, and pages whose inline scripts depend on external ones died on ReferenceErrors with their JS-rendered content missing.

Changes:

• should_block_url consults only Network.setBlockedURLs patterns.
• Static subresource fetches (scripts, stylesheets, stylesheet @imports) matching active interception patterns are paused on the existing InterceptedRequest channel (the one op_fetch_url already uses for fetch()/XHR) and the client's verdict is obeyed: Continue (with URL override), Fail (skip the resource), Fulfill (use the provided response).
• An empty pattern list intercepts everything, matching Fetch.enable's default and the library's enable_interception().
• Fail-open on a closed channel or a client that does not answer within 5s, so a crashed or hung client cannot stall rendering.
• linked_stylesheet_graph_fetches_once_and_preserves_order_and_bases encoded the old semantics (pattern match with no client attached = silent drop); it now attaches an interception client that refuses the matched stylesheet, which is the contract CDP specifies.

Test plan:

• New crates/obscura/tests/subresource_interception.rs: a page with one stylesheet, one external script, and an inline script depending on it; the interception client aborts .css and continues the rest. On main the script never runs and neither request reaches the client; with the fix the script executes, the stylesheet is skipped, and both requests reach the client.
• cargo nextest run -p obscura -p obscura-cdp -p obscura-cli -p obscura-mcp -p obscura-browser: 244 passed, 3 skipped.
• Obstacle course: 32/33, identical to unpatched main (pre-existing observer-intersection failure, see fix(js): bind computed style methods passed through to the declaration #636's test plan).