Using BMesh operators through the edit-mesh API created a full copy of the mesh so it was possible to restore the mesh in case one of the operators raised an error. Remove support for automatic backup/restore from the EDBM_op_* API's as it adds significant overhead and was rarely used. Operators that need this can use the BMBackup API to backup & restore the mesh in case of failure. Add warning levels to BMO_error_raise so operators can report problems without it being interpreted as a request to cancel the operation. For high-poly meshes creating and freeing a full copy is an expensive operation, removing this gives a speedup of ~1.77x for most operators except for "connect_verts" / "connect_vert_pair" which still uses this functionality.