multiple improvements

[vredchenko]

• bugfix: updated database schema: atlas tile to reference grid via grid_uuid FK
• add convenience script to quickly see database row totals
• test EPU agent watcher persists data to DB (not just parser) smartem-devtools#50
• DB connection pooling
• atlas data processing fix
  1. Pydantic Schema: Made description field optional in AtlasData
  2. Parser: Added null checks before accessing atlas_data.gridsquare_positions
  3. Watcher: Applied same defensive checks to runtime atlas processing

./tools/db_table_totals.py 
Database Table Row Counts
========================================
acquisition                                1
atlas                                      1
atlastile                                 35
atlastilegridsquareposition              466
grid                                       2
gridsquare                               466
foilhole                               3,278
micrograph                               606
qualitypredictionmodel                     4
qualitypredictionmodelparameter            0
qualitypredictionmodelweight           3,192
qualityprediction                     14,976
========================================
TOTAL                                 23,027

after fix for atlas tiles processing:

Database Table Row Counts
========================================
acquisition                                1
atlas                                      4
atlastile                                105
atlastilegridsquareposition            1,504
grid                                       4
gridsquare                             2,027
foilhole                              12,473
micrograph                             1,489
qualitypredictionmodel                     4
qualitypredictionmodelparameter            0
qualitypredictionmodelweight          10,212
qualityprediction                     57,308
========================================
TOTAL                                 85,131