Refactor code structure for improved readability and maintainability

src/__Libraries/StellaOps.Infrastructure.Postgres/Migrations/MigrationRunner.cs

@@ -528,3 +528,8 @@ public sealed class MigrationRunner : IMigrationRunner
     private record AppliedMigration(string Name, string Category, string Checksum, DateTimeOffset AppliedAt);
     private record PendingMigration(string Name, MigrationCategory Category, string Checksum, string Content);
 }
+
+/// <summary>
+/// Information about an applied migration.
+/// </summary>
+public readonly record struct MigrationInfo(string Name, DateTimeOffset AppliedAt, string Checksum);