Improve ScheduledTellMsg logging

[Arkatufus]

Fixes #7264

Changes

• Add ToString() overrides for IScheduledTellMsg implementations, basically allows users get some insight into which scheduled messages were being dead lettered.

Turns

[WARNING][06/24/2024 14:51:03.026Z][Thread 0015][akka://ClusterClientDiscoverySpec/user/$b] DeadLetter from [akka://ClusterClientDiscoverySpec/user/$b#1239270490] to [akka://ClusterClientDiscoverySpec/user/$b#1239270490]: <Received dead letter from [akka://ClusterClientDiscoverySpec/user/$b#1239270490]: Akka.Actor.Scheduler.ScheduledTellMsg>

into

[WARNING][06/10/2025 17:28:52.161Z][Thread 0022][akka://ClusterClientDiscoverySpec/user/client1/$b] DeadLetter from [akka://ClusterClientDiscoverySpec/user/client1/$b#1665680760] to [akka://ClusterClientDiscoverySpec/user/client1/$b#1665680760]: <Received dead letter from [akka://ClusterClientDiscoverySpec/user/client1/$b#1665680760]: {ScheduledTellMsg: {Message: Akka.Cluster.Tools.Client.ClusterClient+ReconnectTimeout}}>

[Aaronontheweb]

LGTM