Fix typos, upgrade yarn packages, add some improvements

Why are these changes needed?

[ ] I've included any doc changes needed for https://microsoft.github.io/FLAML/. See https://microsoft.github.io/FLAML/docs/Contribute#documentation to build and test documentation locally.
[ ] I've added tests (if relevant) corresponding to the changes introduced in this PR.
[ ] I've made sure all auto checks have passed.