Conditionally bulk_insert Messages

[an7oine]

Compatibility with e.g. Mysql, where bulk insert does not return generated primary keys.

Summary by Sourcery

Support databases without bulk insert row-returning capability by falling back to individual saves for message creation.

Bug Fixes:

• Ensure compatibility with DBs (e.g. MySQL) that don’t return generated primary keys from bulk insert.

Enhancements:

• Conditionally use bulk_create when the DB can return inserted rows and otherwise save messages individually to assign IDs correctly.