Stack from [ghstack](https://github.com/ezyang/ghstack) (oldest at
bottom):
* #16565
* #16551
* #16469
* #16457
* #16455
* #16454
* #16453
* #16452
* #16451
* #16450
* #16449
* #16448
* #16447
* #16446
* __->__ #16724

Copy CUDAGuard and CUDAStreamGuard from cuda/runtime/ to aoti/slim/cuda/
to support slimtensor requirement while get rid of potential circular
dependency:
- cuda_backend/main_functionalities -> aoti/slimtensor ->
cuda_backend/cuda_guard

This change:
- copy guard.h, guard.cpp and test files from backend/cuda_backend to
backend/aoti/slim/cuda/

Differential Revision:
[D91056808](https://our.internmc.facebook.com/intern/diff/D91056808/)

…v2 (#16446)

Stack from [ghstack](https://github.com/ezyang/ghstack) (oldest at
bottom):
* #16565
* #16551
* #16469
* #16457
* #16455
* #16454
* #16453
* #16452
* #16451
* #16450
* #16449
* #16448
* #16447
* __->__ #16446
* #16724

Add SlimTensor-based implementations of AOTI shim functions for tensor
creation:

1. `aoti_torch_create_tensor_from_blob_v2()` - Creates a non-owning
SlimTensor that wraps existing memory using the `from_blob()` factory

Both functions support CPU and CUDA devices and handle all 7 SlimTensor
dtypes.

Also add `memory_slim.h` and `memory_slim.cpp` with SlimTensor-based
shim implementations for working on new API while not impact the current
pipeline. Will use memory_slim.{h/cpp} to replace current memory.{h/cpp}
when everything has been set up.

Differential Revision:
[D90126247](https://our.internmc.facebook.com/intern/diff/D90126247/)

Stack from [ghstack](https://github.com/ezyang/ghstack) (oldest at
bottom):
* #16565
* #16551
* #16469
* #16457
* #16455
* #16454
* #16453
* #16452
* #16451
* #16450
* #16449
* #16448
* __->__ #16447
* #16446
* #16724

Add SlimTensor-based implementations of AOTI shim functions for tensor
creation:

`aoti_torch_create_tensor_from_blob_v2()` - Creates a non-owning
SlimTensor that wraps existing memory using the `from_blob()` factory

Both functions support CPU and CUDA devices and handle all 7 SlimTensor
dtypes.

Changes:
- Add `memory_slim.h` and `memory_slim.cpp` with SlimTensor-based shim
implementations
- Add `runtime_shims_slim` library target to TARGETS with
`CUDA_AVAILABLE=1` preprocessor flag
- Add `cuda_shim_slim_cpp_unittest()` function for SlimTensor test
targets

Differential Revision:
[D90126244](https://our.internmc.facebook.com/intern/diff/D90126244/)

Pull Request resolved: #16451

Add SlimTensor-based `aoti_torch_copy_()` - Copies data from source tensor to destination tensor. Delegates to SlimTensor's `copy_()` which handles all device combinations (CPU-CPU, CPU-CUDA, CUDA-CPU, CUDA-CUDA).
ghstack-source-id: 336294938
@exported-using-ghexport

Differential Revision: [D90126246](https://our.internmc.facebook.com/intern/diff/D90126246/)

Pull Request resolved: #16451

Add SlimTensor-based `aoti_torch_copy_()` - Copies data from source tensor to destination tensor. Delegates to SlimTensor's `copy_()` which handles all device combinations (CPU-CPU, CPU-CUDA, CUDA-CPU, CUDA-CUDA).
ghstack-source-id: 336304836
@exported-using-ghexport

Differential Revision: [D90126246](https://our.internmc.facebook.com/intern/diff/D90126246/)

Stack from [ghstack](https://github.com/ezyang/ghstack) (oldest at
bottom):
* #16451
* #16450
* #16449
* __->__ #16448

Add `aoti_torch_delete_tensor_object()` - Deletes a tensor object.
SlimTensor uses SharedPtr-based reference counting, so simply deleting
the tensor automatically handles storage deallocation when the last
reference is removed.

Differential Revision:
[D90126248](https://our.internmc.facebook.com/intern/diff/D90126248/)

Stack from [ghstack](https://github.com/ezyang/ghstack) (oldest at
bottom):
* #16451
* #16450
* __->__ #16449
* #16448

Add `aoti_torch_new_tensor_handle()` - Creates a new tensor handle that
shares storage with the original tensor. Uses SlimTensor's copy
constructor which shares the SharedPtr<Storage>, so both tensors
reference the same memory.

Differential Revision:
[D90126245](https://our.internmc.facebook.com/intern/diff/D90126245/)

Stack from [ghstack](https://github.com/ezyang/ghstack) (oldest at
bottom):
* #16453
* #16452
* #16451
* __->__ #16450

Add SlimTensor-based `aoti_torch__reinterpret_tensor()` - Creates a
reinterpreted view of a tensor with new sizes, strides, and storage
offset using SlimTensor's `as_strided()` method. The view shares the
same underlying storage.

Differential Revision:
[D90126249](https://our.internmc.facebook.com/intern/diff/D90126249/)

Stack from [ghstack](https://github.com/ezyang/ghstack) (oldest at
bottom):
* #16453
* __->__ #16452
* #16451
* #16450

Add SlimTensor-based `aoti_torch_assign_tensors_out()` - Creates a new
tensor handle that moves the ownership of storage from the source tensor
to ret tensor via SharedPtr.

Differential Revision:
[D90126243](https://our.internmc.facebook.com/intern/diff/D90126243/)

Stack from [ghstack](https://github.com/ezyang/ghstack) (oldest at
bottom):
* __->__ #16453
* #16452
* #16451
* #16450

Add SlimTensor-based `aoti_torch_item_bool()` - Extracts a boolean
scalar value from a single-element tensor. Uses SlimTensor's
`item<bool>()` which handles CUDA tensors by automatically copying the
value to CPU.

Differential Revision:
[D90126253](https://our.internmc.facebook.com/intern/diff/D90126253/)

This PR was created by the merge bot to help merge the original PR into
the main branch.
ghstack PR number: #16451 by
@Gasoonjia
^ Please use this as the source of truth for the PR details, comments,
and reviews
ghstack PR base:
https://github.com/pytorch/executorch/tree/gh/gasoonjia/93/base
ghstack PR head:
https://github.com/pytorch/executorch/tree/gh/gasoonjia/93/head
Merge bot PR base:
https://github.com/pytorch/executorch/tree/gh/gasoonjia/92/orig
Merge bot PR head:
https://github.com/pytorch/executorch/tree/gh/gasoonjia/93/orig
Differential Revision:
[D90126246](https://our.internmc.facebook.com/intern/diff/D90126246/)
@diff-train-skip-merge

---------

Co-authored-by: gasoonjia <gasoonjia@icloud.com>
Co-authored-by: Gasoonjia <gasoonjia@meta.com>