chore: bump version to 1.171.0 - #9381

Commit 3f86ca3. The PR only bumps the version string in samcli/__init__.py from 1.170.0 to 1.171.0 (+1 -1). There is no new runtime behavior, CLI change, build change or file output to exercise; running sam --version would only echo the new string, which the diff already shows. PLANNER.md classes version bumps as not useful for a hands-on run.