Minor admin improvements and remove unique_together deprecated Meta

Also make rolling stock unique per consist

ram/metadata/migrations/0020_alter_decoderdocument_unique_together_and_more.py

@@ -0,0 +1,33 @@
+# Generated by Django 5.1.4 on 2025-01-08 22:25
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("metadata", "0019_alter_scale_gauge"),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name="decoderdocument",
+            unique_together=set(),
+        ),
+        migrations.AlterUniqueTogether(
+            name="rollingstocktype",
+            unique_together=set(),
+        ),
+        migrations.AddConstraint(
+            model_name="decoderdocument",
+            constraint=models.UniqueConstraint(
+                fields=("decoder", "file"), name="unique_decoder_file"
+            ),
+        ),
+        migrations.AddConstraint(
+            model_name="rollingstocktype",
+            constraint=models.UniqueConstraint(
+                fields=("category", "type"), name="unique_category_type"
+            ),
+        ),
+    ]