Rewrite merge methods on real Core constructs so schema_translate_map applies to loaded data

[nicoloesch]

Summary

Depends on AustralianCancerDataNetwork/oa-configurator#37.

Requires pyproject.toml version update for oa-configurator

Breaking change

OrmLoaderConfig.test_orm_db is gone, replaced by test_orm_db_pg/test_orm_db_sqlite. Anyone
with test_orm_db set in their omop.config will need to update it — there is no back-compat
shim. Needed because dialect-specific integration tests require a guaranteed-correct-dialect test
database each, which one shared field couldn't express.

Root cause

Four related ways schema_translate_map was silently bypassed across orm-loader:
merge_replace/merge_insert/merge_upsert built raw, unqualified text() SQL; staging-table
index inspection used a schema-blind sa.inspect(); materialized-view lifecycle methods took a
hand-threaded schema string instead of resolving through the connection; and a staging-table
reflection path could open a second connection that, on SQLite, silently discarded a session's own
uncommitted work.

Fix

Loaded/merged data

• merge_replace/merge_insert/merge_upsert rewritten against real Table objects and
  dialect-specific Core constructs (sa.delete, insert().from_select(),
  postgresql.insert().on_conflict_do_nothing(), with a SQLite-specific counterpart), for both
  backends.
• Fixed the one remaining raw isolation_level="AUTOCOMMIT" call site.
• Fixed a data-loss bug in staging-table reflection: it now reflects through the session's own
  connection() instead of opening a second one off the bare engine — on SQLite's
  SingletonThreadPool that second connection is the same underlying DBAPI connection, and closing
  it silently discarded the session's own uncommitted work.
• _target_has_rows() simplified: dropped a dead cross-table re-reflection branch.

Materialized views

• create_mv/refresh_mv/drop_mv/index creation are fully role-aware: each resolves its physical
  schema from the bound connection's own schema_translate_map (__mv_role__, defaulting to
  Role.PRIMARY), not a hand-threaded schema parameter.
• The Postgres-only dialect guard is now a single check inside the shared _as_connection()
  context manager (every bind-taking backend method routes through it), replacing a narrower
  per-method check that only ever guarded direct/manual PostgresBackend() construction.
• Staging-table index management (manage_indices) now resolves its Inspector schema-aware, via
  schema_inspect(session, role=role_of_table(cls.__table__)).
• New role_of_table() helper: reads a mapped table's own declared schema tag back as a Role.

Split primary/vocab connections

• Loading and merging now works correctly against genuinely separate primary/vocab connections
  (different engines, potentially different dialects), not just role-tagged schemas on one shared
  connection.

Config, CI, test infrastructure

• STAGING_SCHEMA's reserved-schema registration moved into config.py (the actual omop.config
  entry point), so it's guaranteed to run whenever this package's config is resolvable, instead of
  depending on some other module happening to be imported first.
• OrmLoaderConfig.test_orm_db split into test_orm_db_pg/test_orm_db_sqlite, so dialect-specific
  integration tests always run against the right kind of database regardless of local config.
• CI split into separate SQLite and Postgres build-test jobs (previously one Postgres-only job).
• engine_with_replica_role now uses autocommit_connection()'s Engine branch directly instead of
  opening a connection first and handing it in, removing a redundant step.
• Its own Dialect enum is gone; imports the shared one from oa-configurator instead, with no
  change in dispatch behaviour.
• Adopts oa-configurator's new test infrastructure (isolated_test_database, DIALECT_PARAMS,
  the db_dialect marker).
• New tests: test_schema_translate_map.py (the actual regression test for the originally-reported
  bug), test_split_connection.py, test_shared_backend.py (merge-method contract tests unified
  across both dialects), test_reserved_schema.py (proves STAGING_SCHEMA registration is actually
  enforced cross-package, not just declared).

Checklist

• Applied exactly one label (breaking, feature, fix, dependencies, or chore)
• Tests pass locally (uv run pytest -q): 246 passed, 1 xfailed
• Tests pass locally (uv run pytest -q -m postgresql): 37 passed
• Lint passes (uv run ruff check .)