Add Redshift warehouse adapter

[carolsimone]

Add a Redshift warehouse engine: one WarehouseAdapter implementation, published as continuo-redshift-adapter, with a continuo-python-runtime-redshift base image.

Part of the warehouse-engines rollout tracked in carolsimone/continuo#517. Sibling engines: BigQuery (#57), Snowflake (#58).

Scope

Mirror adapters/postgres/ and adapters/trino/. A new engine is one WarehouseAdapter subclass serving both roles (data plane + validation) and one image that runs both.

• New uv workspace member adapters/redshift/: continuo_redshift_adapter/ (the adapter class), pyproject.toml, tests/, README.md. Add it to [tool.uv.workspace] in the root pyproject.toml.
• Implement the data-plane methods: fetch, ensure_table, load.
• Implement the validation methods: ensure_schema, drop_schema, build_empty_from_sql, build_empty_from_columns, clone_empty_from_prod, check_binds.
• Register the adapter under the continuo_engine.adapters entry-point group (so the runtime discovers it at run time).
• Publish continuo-redshift-adapter on the shared vX.Y.Z tag (wire into publish-pypi.yml).
• Add Dockerfile.redshift + image-requirements-redshift.txt; wire into images.yml → base image continuo-python-runtime-redshift (installs the pinned continuo-redshift-adapter==X.Y.Z).
• Tests: adapter unit tests + the shared adapter conformance suite.

Engine notes

• Wire protocol is postgres-compatible (psycopg / redshift-connector), so adapters/postgres/ is the closest starting point — but the type system and DDL differ, so it is a distinct adapter, not a postgres subclass by default.
• clone_empty_from_prod: CREATE TABLE ... (LIKE prod) is supported.
• Watch for Redshift-specific differences: no true SERIAL/identity parity, COPY-based bulk load, distribution/sort keys, and reduced type coverage vs. Postgres.

Do not touch

The result-block wire contract is frozen (docs/boundary-contract.md, continuo_engine_contract.result). The Go side (pkg/validationresult in carolsimone/continuo) parses it byte-for-byte. Reuse it as-is.

Reference

• adapters/postgres/ (closest — shared wire protocol) and adapters/trino/.
• docs/boundary-contract.md — the external boundary contract.
• continuo-engine-contract (contract/) — the WarehouseAdapter port and the shared SQL/type/config guards.