Summary

Add prose test for listCollections primary-routing rule.

Motivation

The routing MUST clarified by DRIVERS-3481 has no spec test, and existing server selection coverage wouldn't catch the most likely regression, a driver wiring the client's default read preference into listCollections instead of Primary.

Acceptance Criteria

Test 1: listCollections routes to primary in replica set topology

1. Create a command-monitor that captures the ConnectionID of any command with the name listCollections.
2. Create a new client with the command-monitor attached and the read preference set to secondary.
3. Invoke listCollections against the new client and assert that the command succeeded.
4. Verify, via the driver's command-monitoring API, that the operation was issued against the primary node.

Test 2: listCollections succeeds when directly connected to a secondary

1. Construct a client whose URI points at a known secondary and sets directConnection=true.
2. Invoke listCollections and assert that it succeeds.

Go Driver implementation: https://github.com/mongodb/mongo-go-driver/pull/2390