fix: emit Delta liquid clustering for clustered_by (#187)

[mdrakiburrahman]

Closes #187.

Problem

{{ config(clustered_by=[...]) }} is silently a no-op on Delta tables today. fabricspark__clustered_cols only emits the clause when buckets is also set (Hive bucketing). For Delta, the right behavior is to emit CLUSTER BY (cols) for Fabric Spark liquid clustering.

Fix

Drop in the reference impl from #187 — override fabricspark__clustered_cols and fabricspark__file_format_clause so the existing clustered_by config opts a Delta table into liquid clustering. No new config name introduced.

Semantics matrix:

clustered_by	buckets	file_format	partition_by	Result
set	set	any	—	unchanged Hive bucketing: clustered by (cols) into N buckets
set	unset	delta/unset	unset	new: cluster by (cols) + using delta emitted by file_format_clause
set	unset	delta/unset	set	new: compile-time exceptions.raise_compiler_error (mutually exclusive)
set	unset	non-delta	—	unchanged: no clustering clause, using <fmt> emitted
unset	—	any	—	unchanged

Seeds inherit the new behavior automatically through adapter dispatch — seed.sql calls the same clustered_cols and file_format_clause macros.

Expected DDL (per #187 acceptance criteria)

CREATE OR REPLACE TABLE schema.t
USING DELTA
CLUSTER BY (col_a, col_b)
AS SELECT ...

Validation

npx nx run dbt-fabricspark:test ran end-to-end on this branch — all targets green:

Step	Duration	Status
Unit tests (incl. 10 new cluster-by branches)	< 1s	✅
Local-e2e (jaffle_shop, Spark 3.5.1 + Delta 3.2.0)	~6 min	✅
Functional no_schema	14m 7s	✅
Functional with_schema (incl. cross-workspace)	19m 52s	✅
Lint	< 1s	✅
Build + twine	< 5s	✅

End-to-end smoke models added per user direction:

• tests/functional/adapter/persist_docs/fixtures.py::_MODELS__TABLE_DELTA_MODEL → clustered_by=['id'] (Fabric).
• tests/fixtures/dbt-jaffle-shop/models/orders.sql → clustered_by=['order_id'] (local Livy).

A successful dbt run against both Fabric Spark and local Spark+Delta with the new clause is the live confirmation that the macros emit valid liquid-clustering SQL.

Version

Bumps 1.12.0 → 1.12.1, CHANGELOG updated.