Update base for Update on "[slimtensor] Add SlimTensor class with basic properties and CPU copy operation"

**Key components:**

1. **`c10/core/Contiguity.h`** - Contiguity checking utility:
   - `_compute_contiguous<T>()` - computes whether a tensor with given sizes/strides is contiguous in memory (row-major order)

2. **`core/SlimTensor.h`** - Main SlimTensor class with:
   - **Constructors**: Default (undefined tensor) and full constructor with storage, sizes, strides, dtype, and storage_offset
   - **Property accessors**:
     - `sizes()`, `size(dim)` - get tensor dimensions with negative indexing support
     - `strides()`, `stride(dim)` - get tensor strides with negative indexing support
     - `dtype()`, `device()`, `device_type()`, `device_index()`
     - `numel()`, `dim()`, `nbytes()`, `itemsize()`
     - `data_ptr()` - returns pointer to tensor data (adjusted for storage_offset)
     - `storage_offset()`, `storage()`
   - **State queries**: `defined()`, `is_cpu()`, `is_contiguous()`, `is_empty()`
   - **Copy operation**: `copy_(other)` - copies data from another tensor
     - Fast path: uses memcpy for both-contiguous tensors
     - Slow path: element-wise copy respecting strides for non-contiguous tensors
   - **Setters**: `reset()`, `set_storage()`, `set_sizes_and_strides()`

**Curretnt constraints:**
- Only CPU device supported
- Only Float32 dtype tested
- copy_() only supports CPU-to-CPU copy

Those contraints will be further improved in the following diffs

Differential Revision: [D89750150](https://our.internmc.facebook.com/intern/diff/D89750150/)

[ghstack-poisoned]

Author: Gasoonjia

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

@@ -190,7 +190,7 @@ TEST(StorageSharedPtrTest, SharedOwnership) {
   Storage storage1(new MaybeOwningStorage(CPU_DEVICE, kNbytes));
   void* data_ptr = storage1->data();
 
-  Storage storage2 = storage1;  // Copy, not reference - increments ref count
+  Storage storage2 = storage1; // Copy, not reference - increments ref count
 
   EXPECT_EQ(storage1.use_count(), 2);
   EXPECT_EQ(storage2.use_count(), 2);
@@ -227,9 +227,9 @@ TEST(StorageSharedPtrTest, ReferenceCountDecrement) {
   EXPECT_EQ(storage1.use_count(), 1);
 
   {
-    Storage storage2 = storage1;  // Copy increments ref count
+    Storage storage2 = storage1; // Copy increments ref count
     EXPECT_EQ(storage1.use_count(), 2);
-  }  // storage2 destroyed, ref count decrements
+  } // storage2 destroyed, ref count decrements
 
   EXPECT_EQ(storage1.use_count(), 1);
 }