Release 2.4.0

[MichaelGHSeg]

Bumps the version and dates the existing Unreleased changelog section. No code changes.

Releases the HTTP work already on master:

• Improve HTTP response handling and retry logic #520 — improve HTTP response handling and retry logic
• Bound the rate-limit retry budget at 30 minutes #536 — bound the rate-limit retry budget at 30 minutes

Minor rather than patch: sends Authorization and X-Retry-Count request headers that earlier versions did not, and changes retry behaviour — both carry upgrade notes — but nothing is removed from the API.

The version is bumped in both pyproject.toml and segment/analytics/version.py; publish.yml validates the release tag against pyproject.toml and the two must agree.

After merge: tag 2.4.0 (bare, no v) and then create a GitHub Release — publish.yml triggers on release: published, so a tag push alone does not start it. The PyPI trusted publisher is registered and matches (repo segmentio/analytics-python, workflow publish.yml, environment production). The publish job will pause for environment approval.