`create_a_venv` Fails If `venv_path` is a string

[EricLYunqi]

File src/bolo/api.py, line 85 - 94:

    def create_venv(self, repo_id: str, venv_path: str | Path | None = None):
        repo_name = "__SEP__".join(repo_id.split('/'))
        
        if not venv_path:
            venv_path = self.db_dir / "tmp_venv" / repo_name
            print(f"you do not specify the venv path for {repo_id}, we create by default at {venv_path}")
        
        if venv_path.exists():
            print(f"ven for {repo_id} has been already existed")
            return venv_path / "bin" / "python", True

...

Obviously if the venv_path it will throw an run time error since str object does not have exists() function