rename Benchmark.benchmark_type to source, add Result.suite_version

  Repurpose the cryptic C/O codes as full-text 'legacy'/'pyperformance' values.
  Migration remaps all existing rows to 'legacy'. Result.suite_version (blank
  default) records which version of the benchmark suite produced each measurement.
  Remove the clean() constraint that tied default_on_comparison to benchmark_type.

  Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: mattip

codespeed/migrations/0005_benchmark_source_result_suite_version.py

@@ -0,0 +1,36 @@
+from django.db import migrations, models
+
+
+def remap_benchmark_type(apps, schema_editor):
+    Benchmark = apps.get_model('codespeed', 'Benchmark')
+    Benchmark.objects.all().update(source='legacy')
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('codespeed', '0004_branch_display_on_comparison_page'),
+    ]
+
+    operations = [
+        migrations.RenameField(
+            model_name='benchmark',
+            old_name='benchmark_type',
+            new_name='source',
+        ),
+        migrations.RunPython(remap_benchmark_type, migrations.RunPython.noop),
+        migrations.AlterField(
+            model_name='benchmark',
+            name='source',
+            field=models.CharField(
+                choices=[('legacy', 'Legacy'), ('pyperformance', 'PyPerformance')],
+                default='legacy',
+                max_length=14,
+            ),
+        ),
+        migrations.AddField(
+            model_name='result',
+            name='suite_version',
+            field=models.CharField(blank=True, default='', max_length=50),
+        ),
+    ]