[WASM] Integration tests: Hooks system

[awsarron]

Parent issue

strands-agents/sdk-typescript#1104

Scope

Write integration tests validating the hooks/callback system:

• HookRegistry on Agent
• Registering callbacks for specific stream event types
• Callbacks fire at correct lifecycle points (before/after invocation, model call, tool call)
• Multiple callbacks for the same event
• Callback receives correct event data
• Stream event type coverage (text-delta, tool-use, tool-result, stop, error, etc.)

Context

The Python hooks system subscribes to stream events emitted by the WASM guest. Each event arm in the WIT stream-event variant maps to a Python class. Callbacks are registered per-class on the HookRegistry.

Key areas:

• Event dispatch correctly maps WIT variant arms to Python callback classes
• Callback ordering (registration order for "before" events, reverse for "after")
• Event data is correctly deserialized from WIT types

Done when

• Callbacks fire for lifecycle events (invocation, model call, tool call)
• Text-delta and other stream events are receivable via callbacks
• Multiple callbacks per event type work
• Event data contains expected fields
• Callbacks can observe full agent lifecycle end-to-end