Reusable workflows and actions for XRPLF repos

• cleanup-workspace: Cleans up the GitHub Actions workspace, should be used for self-hosted runners before running any steps.
• get-nproc: Retrieves the number of processing units available on the runner.
• prepare-runner: Prepares the GitHub Actions runner environment for subsequent steps.

• pre-commit.yml: Runs pre-commit checks on code changes.
• pre-commit-autoupdate.yml: Runs pre-commit autoupdate to update pre-commit hooks.