Clean up Polars unit tests setup

[mroeschke]

Description

Follow ups to #22048

closes #20551

• Removes some Polars dependency pinnings which should no longer be necessary
• Un-skips some unit tests that should be fixed now

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 648d028 and e95d371.

📒 Files selected for processing (2)

• ci/test_cudf_polars_polars_tests.sh
• python/cudf_polars/cudf_polars/testing/inject_gpu_engine.py

💤 Files with no reviewable changes (2)

• python/cudf_polars/cudf_polars/testing/inject_gpu_engine.py
• ci/test_cudf_polars_polars_tests.sh

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📝 Walkthrough

Summary by CodeRabbit

• Chores

  • Simplified CI test configuration for Polars testing by removing unnecessary dependency management adjustments.
  • Cleaned up testing module by removing outdated development notes.

• Tests

  • Removed three obsolete test skip entries from Polars testing configuration that are no longer needed.

Walkthrough

This PR removes outdated test skip entries and simplifies the Polars CI test environment configuration. The test framework no longer needs to skip three previously flaky upstream Polars tests, and the CI setup no longer applies complex dependency constraint rewrites, instead removing only the polars-cloud dependency.

Changes

Test Infrastructure Cleanup

Layer / File(s)	Summary
CI test environment simplification ci/test_cudf_polars_polars_tests.sh	Replaces multi-sed requirement constraint rewrites for deltalake, pydantic, aiosqlite, pandas, pandas-stubs, and pyparsing with a single sed command that removes the polars-cloud line from Polars dev requirements before installation.
Remove obsolete test skips python/cudf_polars/cudf_polars/testing/inject_gpu_engine.py	Removes a TODO comment and three test skip entries: tests/unit/streaming/test_streaming_group_by.py::test_streaming_group_by_literal[1], tests/unit/io/test_iceberg.py::test_fill_missing_fields_with_identity_partition_values[False], and tests/unit/operations/test_rolling.py::test_rolling_agg_bad_input_types[str].

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Suggested labels

Python, cudf-polars

Suggested reviewers

• TomAugspurger

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main purpose of the PR: cleaning up Polars unit tests setup through dependency removal and test un-skipping.
Description check	✅ Passed	The description is directly related to the changeset, referencing follow-ups to PR #22048, closing issue #20551, and explaining the removal of dependency pinnings and un-skipping of tests.
Linked Issues check	✅ Passed	The PR addresses issue #20551 by removing the skip entry for test_rolling_agg_bad_input_types[str], which is the flaky rolling test mentioned in the linked issue.
Out of Scope Changes check	✅ Passed	All changes are in scope: removing Polars dependency pinnings from the test setup script and un-skipping tests that are now expected to pass based on the linked issue resolution.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[mroeschke]

/merge