Transform agg_time_dimension to lowercase (#379)

### Description
Seeing an
[error](https://dbtlabsmt.datadoghq.com/logs?query=env%3A%2Aprod%2A%20service%3Ametricflow-server%20%40levelname%3AERROR%20-%40channel%3Addtrace.internal.writer.writer%20-%22Exception%20in%20callback%20functools.partial%22%20-%22Unclosed%20connector%22%20-%22Unclosed%20client%20session%22&agg_m=count&agg_m_source=base&agg_t=count&clustering_pattern_field_path=message&cols=host%2Cservice&event=AwAAAZejI8GuonG5mgAAABhBWmVqSTlpTkFBQUJ3XzFKR0RCUHRRQUIAAAAkMDE5N2EzMjYtNWNhOC00ZWI2LWI1ODAtN2E5NDE1OTdjNWFkAAld9Q&fromUser=true&messageDisplay=inline&refresh_mode=sliding&saved-view-id=3577070&storage=hot&stream_sort=desc&viz=stream&from_ts=1750698965459&to_ts=1750785365459&live=true)
in MetricFlow where we can't find the `agg_time_dimension` in the
semantic model because it's uppercased in the `defaults` section but
lowercased (by transformation, presumably) in the `dimensions` section.
This will ensure both are lowercased.

### Checklist

- [x] I have read [the contributing
guide](https://github.com/dbt-labs/dbt-semantic-interfaces/blob/main/CONTRIBUTING.md)
and understand what's expected of me
- [x] I have signed the
[CLA](https://docs.getdbt.com/docs/contributor-license-agreements)
- [ ] This PR includes tests, or tests are not required/relevant for
this PR
- [x] I have run `changie new` to [create a changelog
entry](https://github.com/dbt-labs/dbt-semantic-interfaces/blob/main/CONTRIBUTING.md#adding-a-changelog-entry)

Author: courtneyholcomb

.changes/unreleased/Fixes-20250624-125000.yaml

@@ -0,0 +1,6 @@
+kind: Fixes
+body: Ensure agg_time_dimension is lowercased in the manifest
+time: 2025-06-24T12:50:00.951688-07:00
+custom:
+  Author: courtneyholcomb
+  Issue: "379"

dbt_semantic_interfaces/transformations/names.py

@@ -41,6 +41,8 @@ def _lowercase_semantic_model_elements(semantic_model: PydanticSemanticModel) ->
         if semantic_model.dimensions:
             for dimension in semantic_model.dimensions:
                 dimension.name = dimension.name.lower()
+        if semantic_model.defaults and semantic_model.defaults.agg_time_dimension:
+            semantic_model.defaults.agg_time_dimension = semantic_model.defaults.agg_time_dimension.lower()
 
     @staticmethod
     def _lowercase_top_level_objects(model: PydanticSemanticManifest) -> None:

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "dbt-semantic-interfaces"
-version = "0.8.4"
+version = "0.8.5"
 description = 'The shared semantic layer definitions that dbt-core and MetricFlow use'
 readme = "README.md"
 requires-python = ">=3.8"