docs: add a code sample using bpd.options.bigquery.ordering_mode = "partial"

[tswast]

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Towards internal code change 662899733 🦕

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• samples/snippets/ordering_mode_partial_test.py:22, tag bigquery_bigframes_ordering_mode_partial
• samples/snippets/ordering_mode_partial_test.py:28, tag bigquery_bigframes_ordering_mode_partial_ambiguous_window_warning
• samples/snippets/ordering_mode_partial_test.py:40, tag bigquery_bigframes_ordering_mode_partial_drop_duplicates

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[tswast]

Oops. I merged too soon. #1173 to fix the failing Samples tests.

Since it was only remote function and llm that were failures, I (incorrectly) assumed those were flakes.