Explainer doesn't have visit method for PhysicalLayerSchemaCreationStage

[blecourt-private]

When explaining a plan for which the PhysicalLayerSchemaCreationStage is created the following error is thrown in the logs:

sqlmesh.core.plan.explainer - ERROR - Unexpected stage: PhysicalLayerSchemaCreationStage (explainer.py:134)

Link to code: https://github.com/TobikoData/sqlmesh/blob/main/sqlmesh/core/plan/explainer.py#L134

It seems that the visit method visit_physical_layer_schema_creation_stage() for this stage is missing from explainer.py.

The corresponding method is defined in evaluator.py: visit_physical_layer_schema_creation_stage().

[nkwork9999]

Opened #5925 for this — adds the missing visit_physical_layer_schema_creation_stage to RichExplainerConsole, mirroring the schema derivation in SnapshotEvaluator.create_physical_schemas. test_plan_explain now asserts that no stage is logged as unexpected, which also guards against the same omission for stages added later.