test: add escape for keys when serialize

[NguyenHoangSon96]

Closes Issue

Proposed Changes

• Add escape function for fields when serialized with polars.

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• Tests pass
• Commit messages are conventional
• Sign CLA (if not already signed)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.17%. Comparing base (42620f3) to head (cdfde4e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #202   +/-   ##
=======================================
  Coverage   75.17%   75.17%           
=======================================
  Files          35       35           
  Lines        2417     2417           
=======================================
  Hits         1817     1817           
  Misses        600      600           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull request overview

This PR addresses missing escaping of Polars DataFrame field names (keys) when serializing to InfluxDB line protocol, aligning Polars serialization behavior with line protocol requirements and closing the reported issue.

Changes:

• Escape field keys (column names) during Polars DataFrame serialization to line protocol.
• Add a regression test covering whitespace escaping in tag keys and field keys.
• Update the changelog with the new behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
influxdb_client_3/write_client/client/write/polars_dataframe_serializer.py	Escapes field keys via escape_key() when building the fields portion of line protocol.
tests/test_polars.py	Adds a test asserting proper escaping for whitespace in tag keys and field keys.
CHANGELOG.md	Documents the change in upcoming release notes.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[alespour]

LGTM. Copilot suggests more precise wording in CHANGELOG, but I think it is nitpicking.