Unsqueeze at Any Dimension

[agelas]

Feature description

Implement a more flexible unsqueeze() function that matches the behavior of PyTorch's unsqueeze(). The new function should allow inserting a singleton dimension anywhere in the tensor, as opposed to only prepending.

Feature motivation

The current implementation of unsqueeze() only prepends singleton dimensions. This limitation imposes constraints when manipulating tensor shapes. Having a more flexible unsqueeze operation will increase the usability and compatibility of the library.

(Optional) Suggest a Solution

• Modify the unsqueeze() function to take an additional argument, dim, which indicates the position where the singleton dimension should be inserted. Something like this:

// Before `dim`
dims[0..dim].copy_from_slice(&shape.dims[0..dim]);
// Insert singleton dimension at `dim`
dims[dim] = 1;
// After `dim`
dims[(dim+1)..].copy_from_slice(&shape.dims[dim..]);