chore(main): release 9.18.0

[github-actions]

🤖 I have created a release beep boop

9.18.0 (2026-09-18)

Features

• Add retry state for RETRY-spec backoff (#522) (e734558)
• warn that payload filtering has no effect with FDv2 (#518) (296311f)
• Warn when the SDK is used in a forked process without postfork (#512) (75402e9)

Bug Fixes

• Add async modules to the readthedocs API reference (#513) (f40d3b2)
• Drive repeating tasks from a delay source (9abe8cb)
• Log the cached-data evaluation warning only once per client (#520) (59ce998)
• Repeating task wait duration is no longer reduced by a slow callback duration. (9abe8cb)
• Report a distinct User-Agent for the async client (#516) (514c467)

---

This PR was generated with Release Please. See documentation.

---

Note

Overview
This Release Please PR cuts 9.18.0 by bumping the package version in pyproject.toml, ldclient/version.py, .release-please-manifest.json, and the SDK_VERSION example in PROVENANCE.md, and by adding the 9.18.0 section to CHANGELOG.md.

The changelog documents what ships in this tag (already merged on main): RETRY-spec retry/backoff state, operational warnings (FDv2 payload filtering, fork without postfork), repeating-task scheduling fixes (delay-driven waits, no shrink from slow callbacks), once-per-client cached-data evaluation warnings, a distinct async User-Agent, and Read the Docs coverage for async modules.

^{Reviewed by Cursor Bugbot for commit 8e1d3bc. Bugbot is set up for automated code reviews on this repo. Configure here.}