We currently have Disagg running in leader, follower and switch modes in tets/format. Now, we want to extend the test/format to support multi-mode. 

The overall goal is to have multiple databases with multiple connections, where one acts as the leader/primary and the others act as followers. PALM should be used to manage checkpoint reading and uncheckpointed data, ensuring this information is communicated across leaders and followers.

This ticket covers:

• Investigating how multi-mode can be achieved.
• Building a POC with minimal changes to validate feasibility.
• Producing a clear MVP implementation.

Out of scope:

• Data validation for multi-mode (tracked in WT-15382).
• Fixing any testing bugs discovered during investigation.