Raise ArgumentError for multiple :auto dimensions in reshape

[blasphemetheus]

Nx.reshape with more than one :auto dimension leaked a bare ArithmeticError: after resolving the first :auto, Tuple.product multiplied by the second :auto atom.

Nx.reshape(Nx.iota({12}), {:auto, :auto})
# before: ** (ArithmeticError) bad argument in arithmetic expression
# after:  ** (ArgumentError) only a single :auto dimension is allowed in reshape, got: {:auto, :auto}

🤖 Generated with Claude Code

[blasphemetheus]

this one is more opinionated, but covers a uncovered and unintentional error that would be confusing to run into in the wild

[polvalente]

Maybe worth a pass in Nx.revectorize :target_shape