FullSync Initiate Check when at least one sync session is still active.

[vazois]

This PR ensures that streaming snapshot is initiated only one at least one sync session requires fully synchronization.

[Copilot]

Pull Request Overview

This PR ensures that a full streaming snapshot is initiated only when at least one sync session requires a full synchronization. The changes include:

• Updating the test case to wait for the replica to catch up after validating replica data.
• Modifying the DisklessReplication manager to have PrepareForSync return a boolean indicating whether a full sync is required.
• Introducing a boolean flag within PrepareForSync to conditionally trigger the streaming checkpoint.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
test/Garnet.test.cluster/ReplicationTests/ClusterReplicationDisklessSyncTests.cs	Added wait functionality for replica AOF synchronization in the test.
libs/cluster/Server/Replication/PrimaryOps/DisklessReplication/ReplicationSyncManager.cs	Changed PrepareForSync to return a boolean and conditionally trigger the streaming checkpoint based on active sync sessions.

Comments suppressed due to low confidence (1)

libs/cluster/Server/Replication/PrimaryOps/DisklessReplication/ReplicationSyncManager.cs:219

• [nitpick] Consider renaming the method 'PrepareForSync' to better reflect its boolean return value (e.g., 'ShouldPerformFullSync') to improve code clarity.

async Task<bool> PrepareForSync()