Better detection for conflicting packages (#17623)
In the previous iteration, conflict detection was based on top level
modules. This would work if all namespace packages correctly omitted the
`__init__.py`, but e.g. the nvidia packages include an empty
`nvida/__init__.py`.
Instead, we track overlapping top level modules during installation and
perform conflict analysis after installation, recursing only as far as
necessary.
See https://github.com/astral-sh/uv/pull/13437 for a list of reported
conflicts.
Before:
```
$ uv venv -c -q && uv pip install --preview nvidia-nvjitlink-cu12==12.8.93 nvidia-nvtx-cu12==12.8.90
Resolved 2 packages in 0.99ms
░░░░░░░░░░░░░░░░░░░░ [0/2] Installing wheels... warning: The module `nvidia` is provided by more than one package, which causes an install race condition and can result in a broken module. Consider removing your dependency on either `nvidia-nvtx-cu12` (v12.8.90) or `nvidia-nvjitlink-cu12` (v12.8.93).
Installed 2 packages in 3ms
+ nvidia-nvjitlink-cu12==12.8.93
+ nvidia-nvtx-cu12==12.8.90
```
After:
```
$ uv venv -c -q && cargo run -q pip install --preview nvidia-nvjitlink-cu12==12.8.93 nvidia-nvtx-cu12==12.8.90
Resolved 2 packages in 3ms
Installed 2 packages in 4ms
+ nvidia-nvjitlink-cu12==12.8.93
+ nvidia-nvtx-cu12==12.8.90
```
Still detected true positive:
```
$ uv venv -c -q && cargo run -q pip install --no-progress opencv-python opencv-contrib-python --no-build --no-deps --preview
Resolved 2 packages in 5ms
warning: The file `cv2/__init__.pyi` is provided by more than one package, which causes an install race condition and can result in a broken module. Packages containing the file:
* opencv-contrib-python (opencv_contrib_python-4.13.0.90-cp37-abi3-manylinux_2_28_x86_64.whl)
* opencv-python (opencv_python-4.13.0.90-cp37-abi3-manylinux_2_28_x86_64.whl)
Installed 2 packages in 6ms
+ opencv-contrib-python==4.13.0.90
+ opencv-python==4.13.0.90
```
