Bump optree from 0.16.0 to 0.19.0

Bumps [optree](https://github.com/metaopt/optree) from 0.16.0 to 0.19.0.
- [Release notes](https://github.com/metaopt/optree/releases)
- [Changelog](https://github.com/metaopt/optree/blob/main/CHANGELOG.md)
- [Commits](metaopt/optree@v0.16.0...v0.19.0)

---
updated-dependencies:
- dependency-name: optree
  dependency-version: 0.19.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]