feat(logging): Add request_id to all log entries for correlation

[xilosada]

Problem

Logs lack correlation IDs, making it hard to trace a request through the system:

INFO context_id=abc123 "Executing method"
INFO context_id=abc123 "WASM completed"
// Which request? Multiple concurrent requests have same context_id

Proposed Solution

1. Generate request ID at entry point:

use uuid::Uuid;

async fn handle_request(...) {
    let request_id = Uuid::new_v4();
    let span = tracing::info_span!("request", %request_id, %context_id);
    
    async move {
        // All logs within this span include request_id
    }.instrument(span).await
}

2. Propagate through async boundaries:

tokio::spawn(async move {
    // Inherit parent span
}.instrument(tracing::Span::current()));

Acceptance Criteria

• All JSON-RPC requests have unique request_id
• request_id appears in all related logs
• Spans propagate through async tasks
• Can filter logs by request_id

Estimated Effort: 2-4 hours

Priority: P1 (Quick Win)