Add SharedArrayBuffer/COOP-COEP verification for WASM streaming

[noahgift]

Problem

WASM applications using SharedArrayBuffer (required for multi-threaded WASM) need Cross-Origin-Opener-Policy (COOP) and Cross-Origin-Embedder-Policy (COEP) headers. Currently there's no way to:

1. Verify COOP/COEP headers are correctly set
2. Test that SharedArrayBuffer is available in the page context
3. Validate Web Worker communication works

Proposed Solution

Add WasmCapabilities verification:

pub struct WasmCapabilities {
    pub shared_array_buffer: bool,
    pub atomics: bool,
    pub threads: bool,
    pub simd: bool,
}

impl WasmCapabilities {
    /// Check browser capabilities via CDP
    pub async fn detect(page: &Page) -> ProbarResult<Self>;
    
    /// Assert required capabilities are available
    pub fn assert_streaming_ready(&self) -> ProbarResult<()> {
        if !self.shared_array_buffer {
            return Err(ProbarError::MissingCapability(
                "SharedArrayBuffer not available. Check COOP/COEP headers."
            ));
        }
        Ok(())
    }
}

Use Cases

1. Streaming WASM Apps: whisper.apr requires SharedArrayBuffer for audio processing
2. COOP/COEP Header Validation: Ensure server is correctly configured
3. Capability Detection: Skip tests that require unavailable features

Related

• Issue Add AudioEmulator for microphone/getUserMedia testing #12 (AudioEmulator) - streaming audio tests need this too
• probar serve --cross-origin-isolated sets these headers

[noahgift]

Triage: P3 — WASM testing feature. SharedArrayBuffer/COOP-COEP verification for WASM streaming. Part of WASM UX testing epic (#14).