support for i32 type

[michaelfeil]

The case why i32 is required.

I would like to use candle to write bindings to popular kernels and frameworks (examples are: candle-flash-attn-v3, tensorrt bindings). The input requires e.g. i32 (instead of u32) dtype.

example:

• https://github.com/michaelfeil/candle-flash-attn-v3/blob/main/src/lib.rs#L443C9-L446C11

A simple interface for:

• data_ptr()
• shape()