fix: honor expression on primary_key constraints in V1 materialization

[sd-db]

What

On the V1 materialization path (use_materialization_v2: false, the default), the persist_constraints flow rendered primary key(<cols>) and silently dropped the constraint's expression. A primary key declared with expression: RELY (or any trailing clause) was created without it — no error, no warning.

The V2 path (PrimaryKeyConstraint._render_suffix) and V1's own foreign_key branch already honor expression. This change makes the V1 primary_key branch in relations/constraints.sql append expression as a trailing suffix, gated on its presence so a PK without an expression renders identically to before.

Why

PRIMARY KEY (id) RELY is valid Databricks syntax for an informational primary key the optimizer can rely on. Before this fix, the only way to attach RELY at model-build time on the default path was a post-hook.

Given (default path, contract.enforced: true):

constraints:
  - type: primary_key
    columns: [id]
    expression: RELY

• Before: ALTER TABLE … ADD CONSTRAINT pk PRIMARY KEY (id); ← RELY dropped
• After: ALTER TABLE … ADD CONSTRAINT pk PRIMARY KEY (id) RELY;

Tests

• Added test_macros_get_constraint_sql_primary_key_with_expression (tests/unit/macros/relations/test_constraint_macros.py) asserting the rendered SQL carries the expression suffix. Fails without the fix, passes with it.
• PKs without an expression render byte-identically, so the pre-existing constraint macro unit tests are unchanged — full unit suite green.
• Existing constraints/ + persist_constraints/ functional suites pass on a UC SQL warehouse (39 passed).

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Coverage report

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[sd-db]

/integration-test

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Integration tests dispatched for PR #1551 by @sd-db. Track progress in the Actions tab.

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Integration results for PR #1551 — UC cluster ✅ success · SQL warehouse ❌ failure · All-purpose cluster ✅ success · Shard coverage ✅ success

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[github-actions]

Integration results for PR #1551 — UC cluster ✅ success · SQL warehouse ✅ success · All-purpose cluster ✅ success · Shard coverage ✅ success

Run details.