fix: translate MySQL error 3730 to IntegrityError (#1032) (#1319)

When dropping a table/schema referenced by foreign key constraints,
MySQL returns error 3730. This was passing through as a raw pymysql
OperationalError, making it difficult for users to catch and handle.

Now translates to datajoint.errors.IntegrityError, consistent with
other foreign key constraint errors (1217, 1451, 1452).

Before:
  pymysql.err.OperationalError: (3730, "Cannot drop table...")

After:
  datajoint.errors.IntegrityError: Cannot drop table '#table'
  referenced by a foreign key constraint...

Fixes #1032

Co-authored-by: Claude Opus 4.5 <[email protected]>

Author: dimitri-yatsenko

src/datajoint/connection.py

@@ -66,7 +66,11 @@ def translate_query_error(client_error: Exception, query: str) -> Exception:
         # Integrity errors
         case 1062:
             return errors.DuplicateError(*args)
-        case 1217 | 1451 | 1452:
+        case 1217 | 1451 | 1452 | 3730:
+            # 1217: Cannot delete parent row (FK constraint)
+            # 1451: Cannot delete/update parent row (FK constraint)
+            # 1452: Cannot add/update child row (FK constraint)
+            # 3730: Cannot drop table referenced by FK constraint
             return errors.IntegrityError(*args)
 
         # Syntax errors