chore: Bump version to 2.1.0a1 for PostgreSQL multi-backend support

This version includes:
- Database adapter pattern for MySQL/PostgreSQL abstraction
- Full PostgreSQL support as alternative backend
- Backend-agnostic SQL generation throughout codebase

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/version.py

@@ -1,4 +1,4 @@
 # version bump auto managed by Github Actions:
 # label_prs.yaml(prep), release.yaml(bump), post_release.yaml(edit)
 # manually set this version will be eventually overwritten by the above actions
-__version__ = "2.0.0a22"
+__version__ = "2.1.0a1"