feat(cli): add keep_latest prune strategy to ThreadTTLConfig (#6784)

## Summary
- Add `"keep_latest"` to `ThreadTTLConfig.strategy` to match
langgraph-api support for pruning old checkpoints while retaining the
thread and its latest state
- Add `sweep_limit` to `ThreadTTLConfig` where the API actually reads it
(was previously a no-op on `CheckpointerConfig`)
- Regenerate `schema.json` / `schema.v0.json`

## Test plan
- [x] `make format && make lint` passes
- [x] `make test` passes (85/85)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

libs/cli/examples/graph_prerelease_reqs/deps/additional_deps/pyproject.toml

@@ -5,5 +5,5 @@ description = "Test for prerelease stuff"
 readme = "README.md"
 requires-python = ">=3.10"
 dependencies = [
-  "langgraph==1.0.2"
+  "langgraph==1.0.8"
 ]

libs/cli/examples/graph_prerelease_reqs/pyproject.toml

@@ -7,7 +7,7 @@ requires-python = ">=3.10"
 dependencies = [
   "langchain-openai==1.0.0a2",
   "langchain-anthropic==1.0.0a5",
-  "langgraph==1.0.2"
+  "langgraph==1.0.8"
 ]
 
 [tool.uv]