maps.Mesh warning when passing it a string ?

[OrenLeung]

i think it would be good to warning if a user passed into a string into maps.Mesh

mesh = maps.Mesh(devices, ("dp")) # forgot the comma
print(mesh.axis_names)

results in

('d','p')

due to the tuple function at https://github.com/google/jax/blob/main/jax/interpreters/pxla.py#L2324

I can see it as a very common mistake that users run into and spend 15 mins debugging (i fell victim to forgetting a comma)

Proper Code without mistake

mesh = maps.Mesh(devices, ("dp",)) 
print(mesh.axis_names)

results in

('dp')

[sharadmv]

I think we can just convert a string input to a singleton tuple (see #13213)