Migrated all serialization and deserialization from Newtonsoft.Json to System.Text.Json across the codebase for improved performance and reduced dependencies. Updated package references and refactored helper method names for consistency (e.g., IsEmpty, NotEmpty, InRange). Also updated NuGet package versions in project files.
datastore can now prefetch display names (note the first time it sees a avatar the display name will be ?)
the relay service can now talk to rabbit as a target
the relay service can now use an extended output json
