[build] modernize build-frontend: python setup.py develop/install -> [uv ]pip install --no-build-isolation [-e ]. (#156027)

Modernize the development installation:

```bash
# python setup.py develop
python -m pip install --no-build-isolation -e .

# python setup.py install
python -m pip install --no-build-isolation .
```

Now, the `python setup.py develop` is a wrapper around `python -m pip install -e .` since `setuptools>=80.0`:

- pypa/setuptools#4955

`python setup.py install` is deprecated and will emit a warning during run. The warning will become an error on October 31, 2025.

- 9c4d383631/setuptools/command/install.py (L58-L67)

> ```python
> SetuptoolsDeprecationWarning.emit(
>     "setup.py install is deprecated.",
>     """
>     Please avoid running ``setup.py`` directly.
>     Instead, use pypa/build, pypa/installer or other
>     standards-based tools.
>     """,
>     see_url="https://blog.ganssle.io/articles/2021/10/setup-py-deprecated.html",
>     due_date=(2025, 10, 31),
> )
> ```

- pypa/setuptools#3849

Additional Resource:

- [Why you shouldn't invoke setup.py directly](https://blog.ganssle.io/articles/2021/10/setup-py-deprecated.html)

Pull Request resolved: https://github.com/pytorch/pytorch/pull/156027
Approved by: https://github.com/ezyang

README.md

@@ -228,6 +228,7 @@ If you want to disable Intel GPU support, export the environment variable `USE_X
 Other potentially useful environment variables may be found in `setup.py`.
 
 #### Get the PyTorch Source
+
 ```bash
 git clone https://github.com/pytorch/pytorch
 cd pytorch
@@ -279,24 +280,29 @@ conda install -c conda-forge libuv=1.39
 ```
 
 #### Install PyTorch
+
 **On Linux**
 
 If you're compiling for AMD ROCm then first run this command:
+
 ```bash
 # Only run this if you're compiling for ROCm
 python tools/amd_build/build_amd.py
 ```
 
 Install PyTorch
+
 ```bash
 export CMAKE_PREFIX_PATH="${CONDA_PREFIX:-'$(dirname $(which conda))/../'}:${CMAKE_PREFIX_PATH}"
-python setup.py develop
+python -m pip install -r requirements.txt
+python -m pip install --no-build-isolation -v -e .
 ```
 
 **On macOS**
 
 ```bash
-python3 setup.py develop
+python -m pip install -r requirements.txt
+python -m pip install --no-build-isolation -v -e .
 ```
 
 **On Windows**
@@ -308,7 +314,7 @@ If you want to build legacy python code, please refer to [Building on legacy cod
 In this mode PyTorch computations will run on your CPU, not your GPU.
 
 ```cmd
-python setup.py develop
+python -m pip install --no-build-isolation -v -e .
 ```
 
 Note on OpenMP: The desired OpenMP implementation is Intel OpenMP (iomp). In order to link against iomp, you'll need to manually download the library and set up the building environment by tweaking `CMAKE_INCLUDE_PATH` and `LIB`. The instruction [here](https://github.com/pytorch/pytorch/blob/main/docs/source/notes/windows.rst#building-from-source) is an example for setting up both MKL and Intel OpenMP. Without these configurations for CMake, Microsoft Visual C OpenMP runtime (vcomp) will be used.
@@ -329,7 +335,6 @@ Additional libraries such as
 
 You can refer to the [build_pytorch.bat](https://github.com/pytorch/pytorch/blob/main/.ci/pytorch/win-test-helpers/build_pytorch.bat) script for some other environment variables configurations
 
-
 ```cmd
 cmd
 
@@ -349,8 +354,7 @@ for /f "usebackq tokens=*" %i in (`"%ProgramFiles(x86)%\Microsoft Visual Studio\
 :: [Optional] If you want to override the CUDA host compiler
 set CUDAHOSTCXX=C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.27.29110\bin\HostX64\x64\cl.exe
 
-python setup.py develop
-
+python -m pip install --no-build-isolation -v -e .
 ```
 
 **Intel GPU builds**
@@ -372,7 +376,7 @@ if defined CMAKE_PREFIX_PATH (
     set "CMAKE_PREFIX_PATH=%CONDA_PREFIX%\Library"
 )
 
-python setup.py develop
+python -m pip install --no-build-isolation -v -e .
 ```
 
 ##### Adjust Build Options (Optional)
@@ -382,6 +386,7 @@ the following. For example, adjusting the pre-detected directories for CuDNN or
 with such a step.
 
 On Linux
+
 ```bash
 export CMAKE_PREFIX_PATH="${CONDA_PREFIX:-'$(dirname $(which conda))/../'}:${CMAKE_PREFIX_PATH}"
 CMAKE_ONLY=1 python setup.py build
@@ -389,6 +394,7 @@ ccmake build  # or cmake-gui build
 ```
 
 On macOS
+
 ```bash
 export CMAKE_PREFIX_PATH="${CONDA_PREFIX:-'$(dirname $(which conda))/../'}:${CMAKE_PREFIX_PATH}"
 MACOSX_DEPLOYMENT_TARGET=10.9 CC=clang CXX=clang++ CMAKE_ONLY=1 python setup.py build