feat: add embedded chDB driver (driver: chdb)

[wudidapaopao]

Summary

Adds an experimental driver: chdb that runs dbt against chDB — ClickHouse as an in-process engine — with no server, Docker.

Continues the work started in #369 and closes #297. It builds on clickhouse-connect's pluggable backend (ClickHouse/clickhouse-connect#872, released in 1.6.0), which exposes the chDB engine behind get_client(interface="chdb") — so the driver reuses the existing HTTP client surface and only changes how the connection is created.

Also fixes clickhouse__drop_relation so it drops temporary tables. This affects all drivers.

Usage

pip install "dbt-clickhouse[chdb]"

my_project:
  target: ci
  outputs:
    ci:
      type: clickhouse
      driver: chdb
      chdb_path: .chdb   # data directory; ':memory:' (default) for ephemeral
      schema: my_db
    prod:                # production still points at a real server
      type: clickhouse
      driver: http
      host: ...

The embedded engine is single-node, so cluster, cluster_mode, Replicated, and the distributed materializations are rejected. The full integration suite runs against the driver in a new no-Docker CI job (DBT_CH_TEST_DRIVER=chdb).

Checklist

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG

[wudidapaopao]

Hi @BentsiLeviav @koletzilla, this revives #369. With the built-in chDB backend in clickhouse-connect 1.6.0 (ClickHouse/clickhouse-connect#872), wiring chDB into dbt is now much simpler — the driver reuses the existing client surface and only swaps how the connection is created.

Would appreciate a review when you have a chance.

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