randomly generate fake emails

[vdheera]

References the issue here: https://www.google.com/url?q=https://github.com/heartcombo/devise/issues/5498&sa=D&source=docs&ust=1701833326557472&usg=AOvVaw0rlCheHzI9Iz_DlsFU3z3V

whereby, the user emails violated a potential unique constraint on emails. We can fix this by creating our own fixtures to run devise test cases.