feat: Support CDP evaluation in Web Worker contexts

[glamberson]

Use Case

I'm building a performance testing tool for a WASM application that runs its core logic in a Web Worker. The Worker uses WebCodecs VideoDecoder for H.264 decode and exposes metrics via a JS API. I need to:

1. Detect Worker targets when they spawn
2. Evaluate JavaScript in the Worker context to read performance metrics
3. Optionally listen for console messages from Workers

This is a common pattern for any application using Web Workers: PWAs, video players, WASM-heavy apps, etc.

Current Behavior

chromiumoxide currently cannot interact with Worker targets:

1. Service workers are auto-detached: on_event() in handler/target.rs immediately detaches "service_worker" targets on attachment
2. Non-page targets skip initialization: poll() returns None for !self.is_page(), so Workers never reach Initialized state
3. No public API for Worker sessions: Browser::execute() sends with session_id: None (browser-level only)

The TargetType enum already has ServiceWorker, SharedWorker, and BackgroundPage variants with is_*() methods, suggesting this was anticipated but not implemented.

How Puppeteer/Playwright Handle This

Both tools implement Worker evaluation using standard CDP:

Target.setAutoAttach { autoAttach: true, flatten: true, waitForDebuggerOnStart: false }
  -> attachedToTarget event (targetInfo.type == "worker")
  -> sessionId for the Worker
  -> Runtime.evaluate on that sessionId

Chrome CDP fully supports this. The limitation is purely in chromiumoxide's abstraction layer.

Proposed Changes

1. Remove auto-detach for service workers in on_event(), or make it configurable
2. Generalize poll() initialization: allow non-page targets to reach a basic Initialized state (they don't need frame/network/emulation init, just Runtime)
3. Expose Worker session API, something like:

// Get Worker targets
let workers = page.workers().await?;

// Evaluate JS in a Worker
let result = worker.evaluate("self.performance_stats()").await?;

The internal transport already supports session routing via CommandMessage::with_session(). The session_id flows correctly through conn.rs. The change is in the public API surface and initialization pipeline.

Alternatives Considered

• MessageChannel bridge: Worker posts to main page, evaluate on page context. Works but adds latency and indirection.
• Raw WebSocket to CDP: bypass chromiumoxide entirely for Worker commands. Works but defeats the purpose of using the library.
• Fork: would rather contribute upstream if there's interest.

Environment

• chromiumoxide v0.9.1
• Chrome 133+
• Using Workers for WASM (wasm-bindgen) with WebCodecs VideoDecoder

Happy to submit a PR if there's interest in this feature.