fix(python): isolate datadog config defaults

[hcthakur2004]

Summary

• replace shared Datadog config dictionary defaults with per-instance factories
• add regression coverage for retry and async transport rule defaults

Issue

Fixes #4585

Tests

• uv run pytest tests/test_datadog.py
• uv run ruff check src/openlineage/client/transport/datadog.py tests/test_datadog.py

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.87%. Comparing base (169ce36) to head (5437bbc).
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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4586   +/-   ##
=======================================
  Coverage   73.87%   73.87%           
=======================================
  Files          21       21           
  Lines        2354     2354           
=======================================
  Hits         1739     1739           
  Misses        615      615           

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[mobuchowski]

@hcthakur2004 mind making this ready for review so we can merge it?

[hcthakur2004]

@hcthakur2004 mind making this ready for review so we can merge it?

Done, thanks!

[Copilot]

Pull request overview

This PR fixes a Python client bug where DatadogConfig used shared mutable dictionary defaults (retry and async_transport_rules), causing mutations in one config instance to leak into others. It aligns DatadogConfig with safe per-instance default behavior and adds regression tests to prevent reintroduction.

Changes:

• Replaced mutable attr.field(default=...) dict defaults in DatadogConfig with per-instance factories.
• Added regression tests ensuring retry and async_transport_rules defaults are not shared between instances.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
client/python/src/openlineage/client/transport/datadog.py	Introduces factory functions for retry and async_transport_rules to avoid shared mutable defaults across DatadogConfig instances.
client/python/tests/test_datadog.py	Adds regression tests verifying per-instance isolation for default retry config and async transport rules.

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