- Add 4 unit tests for setUpAge() skip_load behavior:
  skip_load=True skips LOAD, skip_load=False executes LOAD,
  load_from_plugins integration, and search_path always set.
- Document skip_load in README under new "Managed PostgreSQL Usage"
  section for Azure/AWS RDS/etc. environments.
- Fix syntax in existing load_from_plugins code example.

Made-with: Cursor

- Raise ValueError when skip_load=True and load_from_plugins=True are
  both set (contradictory combination)
- Add end-to-end test verifying skip_load is forwarded through the full
  age.connect() → Age.connect() → setUpAge() call chain
- Replace fragile string assertions with assert_called_with/assert_any_call
- README: mention configure_connection() as the pool-based alternative
  for managed PostgreSQL environments

Made-with: Cursor

configure_connection() is not part of this PR; use the available
setUpAge() API with skip_load=True for the connection pool example.

Made-with: Cursor