Does NetSuite have a native method for version control / branching?

Nope nothing like that, best practice to have your repo outside of netsuite so you have file history and changes over time there

we use the sdf framework which can be setup with Github actions, so on push to master or pull request it validates and submits to netsuite . You now have to commit history to rollback if needed

Nothing native. I just use git for my version control, and SDF for testing/validating/deploying.