Runtime Adapter Integration

[lxsaah]

Async error handling for Tokio (std) and Embassy (embedded) runtimes.

Acceptance Criteria

• Tokio adapter with timeout error handling
• Embassy adapter with embassy-time integration
• Async error propagation preserves tracing context
• Feature-gated compilation for each runtime

Key Implementation

#[cfg(feature = "tokio-runtime")]
impl TokioAdapter {
    pub async fn execute_with_timeout<F, T>(&self, future: F, timeout_ms: u64) -> DbResult<T>
}

#[cfg(feature = "embassy-runtime")]
impl EmbassyAdapter {
    pub async fn execute_task<F, T>(&self, task: F) -> DbResult<T>
}