SQLAlchemy query caching

[achimnol]

Aside #2546, let's also consider activating SQL-level caches in SQLAlchemy.

We need to check:

• Compatibility with asyncio
• Compatibility with the core API in addition to ORM
• Consistent cache-key representation of SQL statements
  (e.g., Does it use the same cache entry for the same query with differently-ordered columns in the WHERE clause?)
• Potential complexity for SQLAlchemy v2.0 migration

Candidates:

• https://docs.sqlalchemy.org/en/20/orm/examples.html#module-examples.dogpile_caching
• https://dogpilecache.sqlalchemy.org/en/latest/