[cathleeny]

Summary

Bump version to 4.9.0 and add the 4.9.0 section to CHANGELOG.md.

Notable changes since v4.8.0

• Upgrade Databricks SQL Kernel to 1.4.0, which keeps Lakehouse Real-Time session affinity and flushes shared telemetry only after the final session closes.
• Preserve the originating session when re-fetching or concurrently polling async statements on the kernel backend.

Test plan

• pytest tests/unit -m "not realkernel" passes locally (1,266 passed) with the real databricks-sql-kernel 1.4.0 wheel installed, plus tests/unit/test_session.py -m realkernel (2 passed) in a separate process
• Multi-DBR tests in universe/peco/correctness/python passed against the 4.9.0 wheel on DBR 18.3 Photon (PythonSuite thrift + SEA, PythonUnityCatalogSuite thrift, PythonTransactionSuite thrift); tracked in databricks-eng/universe#2977887
• CI green

This pull request and its description were written by Isaac.

[peco-review-bot]

✅ No issues identified by the review bot.