Py3k fix for #2506.

Add 'Blob.compose' API wrapper method.

…ose-py3k-fix

Py3k fix for googleapis#2506.

Add 'Blob.compose' API wrapper method.

The .describe() method attempts to compute metrics like mean, max, and
unique on all columns. For MM complex types (structs representing
images/videos), running COUNT(DISTINCT column) or mathematical
aggregates is physically prohibited by BigQuery and raises syntax/type
validation errors.

We limit aggregations on OBJ_REF_DTYPE and JSON columns to only a basic
.count(), skipping unhashable/unsupported summary metrics.

Fixes #<452681068> 🦕

PR created by the Librarian CLI to initialize a release. Merging this PR
will auto trigger a release.

Librarian Version: v0.8.3
Language Image:
us-central1-docker.pkg.dev/cloud-sdk-librarian-prod/images-prod/python-librarian-generator@sha256:160860d189ff1c2f7515638478823712fa5b243e27ccc33a2728669fa1e2ed0c
<details><summary>bigframes: v2.38.0</summary>

##
[v2.38.0](google/bigframes@v2.37.0...v2.38.0)
(2026-03-16)

### Features

* Add `bigframes.bigquery.rand()` function (#2501)
([5c43efb7](google/bigframes@5c43efb7))

* add `df.bigquery` pandas accessor (#2513)
([91b6c245](google/bigframes@91b6c245))

* Add str, dt accessors to pd.col Expression objects (#2488)
([ce5de570](google/bigframes@ce5de570))

* add bigquery.ml.get_insights function (#2493)
([d29a6095](google/bigframes@d29a6095))

* use EUC for AI IF, CLASSIFY, and SCORE when connection is not provided
(#2507)
([fe94910a](google/bigframes@fe94910a))

### Bug Fixes

* handle unsupported types and empty results in describe (#2506)
([2326ad6a](google/bigframes@2326ad6a))

* no longer automatically use anywidget in the `%%bqsql` magics (#2504)
([43353e2b](google/bigframes@43353e2b))

### Documentation

* Fix typo in ExperimentOptions class docstring (#2498)
([077cb2eb](google/bigframes@077cb2eb))

* add notebooks to user guide page (#2505)
([5cf37888](google/bigframes@5cf37888))

</details>