Update base for Update on "[slimtensor] Add from_etensor factory function for ETensor to SlimTensor conversion"

Add from_etensor() factory function that creates a SlimTensor from an ExecuTorch portable tensor (ETensor), copying data to a target device.

Key features:
- Handles int32_t to int64_t conversion for sizes/strides (ETensor uses int32_t, SlimTensor uses int64_t)
- Supports CPU and CUDA target devices via storage()->copy_()
- Preserves tensor strides (non-contiguous layouts)
- Provides both reference and pointer overloads

Differential Revision: [D90539554](https://our.internmc.facebook.com/intern/diff/D90539554/)

[ghstack-poisoned]

Author: Gasoonjia

backends/aoti/slim/core/test/test_slimtensor_copy.cpp

@@ -11,7 +11,6 @@
 #include <executorch/backends/aoti/slim/core/slim_tensor.h>
 #include <executorch/backends/aoti/slim/core/storage.h>
 
-
 namespace executorch::backends::aoti::slim {
 
 // Helper function to create a CPU storage with given size