Bump turbopuffer from 0.1.15 to 0.1.21

Bumps [turbopuffer](https://github.com/turbopuffer/turbopuffer-python) from 0.1.15 to 0.1.21.
- [Release notes](https://github.com/turbopuffer/turbopuffer-python/releases)
- [Changelog](https://github.com/turbopuffer/turbopuffer-python/blob/main/RELEASE.md)
- [Commits](https://github.com/turbopuffer/turbopuffer-python/commits)

---
updated-dependencies:
- dependency-name: turbopuffer
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

pyproject.toml

@@ -66,7 +66,7 @@ audio = [
 ]
 video = ["opencv-python >= 4.5"]
 
-slackbot = ["marvin[prefect]", "numpy", "raggy", "turbopuffer==0.1.15"]
+slackbot = ["marvin[prefect]", "numpy", "raggy", "turbopuffer==0.1.21"]
 
 [project.urls]
 Code = "https://github.com/prefecthq/marvin"