feature: add optimize() call to snapshot materialization (#1335)

[aarushisingh04]

partially resolves #1335

Description

1. added optimize() call to the snapshot materialization, matching existing behavior in table and incremental materializations. when a snapshot is configured with liquid_clustered_by, zorder, or auto_liquid_cluster, the OPTIMIZE query will now execute automatically after each snapshot run.

2. the change is a single-line addition to snapshot.sql, placed after persist_constraints and before post-hooks (again, consistent with the pattern in table.sql and incremental.sql).

note: the original issue also mentioned default clustering columns and ALTER TABLE support for config changes. these are intentionally excluded from this PR to keep scope minimal and can be addressed in follow-up PRs if needed. i believe they need a design decision that should be discussed by/with maintainers first due to having a larger scope.

Checklist

• I have run this code in development and it appears to resolve the stated issue (unit tests pass : this change mirrors the identical optimize() call pattern already used in table.sql and incremental.sql.)
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the CHANGELOG.md and added information about my change to the "dbt-databricks next" section.

[sd-db]

Overall the change looks good, one think I would look to add is: a functional test for the snapshot + liquid clustering path. Since this changes default behaviour for all liquid-clustered snapshot tables, we should verify the full lifecycle (create + re-snapshot with updates) works correctly with clustering enabled. The "clustering off" path is already covered by the existing TestSnapshot and TestSnapshotCheck tests.This should be straightforward — just extend BaseSimpleSnapshot with liquid_clustered_by configured:

# In tests/functional/adapter/simple_snapshot/test_snapshot.py

@pytest.mark.skip_profile("databricks_uc_cluster", "databricks_cluster")
class TestSnapshotLiquidClustering(BaseSimpleSnapshot):
    @pytest.fixture(scope="class")
    def project_config_update(self):
        return {"snapshots": {"+liquid_clustered_by": "id"}}

This inherits the full snapshot lifecycle test and confirms the behavior is preserved with optimize running

[aarushisingh04]

@sd-db agreed, added the required functional test in test_snapshot.py. thanks for the review!

[sd-db]

looks good, thx for the PR !!