Resolve sqlalchemy deprecation warning

[JeremyMcCormick]

Import declarative_base from new module to resolve sqlalchemy deprecation warning.

Warning message was:

felis/tap.py:44: MovedIn20Warning: The ``declarative_base()`` function is now available as sqlalchemy.orm.declarative_base(). (deprecated since: 2.0) (Background on SQLAlchemy 2.0 at: https://sqlalche.me/e/b8d9)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (32cef69) 93.36% compared to head (3d265f8) 93.36%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #42      +/-   ##
==========================================
- Coverage   93.36%   93.36%   -0.01%     
==========================================
  Files          20       20              
  Lines        2110     2109       -1     
  Branches      425      425              
==========================================
- Hits         1970     1969       -1     
  Misses         81       81              
  Partials       59       59              

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[andy-slac]

Looks good. General comment - in middleware we are avoiding the use of SQLAlchemy ORM, and only using core part of it. I guess a limited use of ORM in felis should be fine.