Function getNthMostRecentBoundary

getNthMostRecentBoundary(
chat_id: string,
depth: number,
): Promise<null | { ts_seconds: number; message_id: string }>
Gets metadata about the Nth most recent message in a specific chat.

This function is used to implement "depth-based" filtering, where you want to import only the most recent N messages from a chat. It's useful for:
- Limiting import scope to recent activity
- Testing with a subset of data
- Incremental imports focusing on recent messages
Parameters
- chat_id: string
  The chat ID to get the boundary message for
- depth: number
  How many messages back from the latest to go (1 = second most recent)
Returns Promise<null | { ts_seconds: number; message_id: string }>
Promise resolving to message metadata or null if fewer than depth+1 messages exist
Example
```
// Get the 100th most recent message (start import from there)
const boundary = await getNthMostRecentBoundary("19175769740@s.whatsapp.net", 100);
if (boundary) {
  console.log(`Importing from message ${boundary.message_id} onwards`);
}
```
- Defined in evolution/reader.ts:180