Add GraalPy support (#5141)

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## Summary

Currently, `uv` refuses to install anything on GraalPy. This is
currently blocking GraalPy testing with cibuildwheel, since manylinux
includes both `uv` and `graalpy` (but doesn't test with `uv`), whereas
cibuildwheel defaults to `uv`. See e.g.
2750618295
where it gives
```
      + python -m build /project/sample_proj --wheel --outdir=/tmp/cibuildwheel/built_wheel --installer=uv
  * Creating isolated environment: venv+uv...
  * Using external uv from /usr/local/bin/uv
  * Installing packages in isolated environment:
    - setuptools >= 40.8.0
  > /usr/local/bin/uv pip install "setuptools >= 40.8.0"
  < error: Unknown implementation: `graalpy`
```

## Test Plan

I simply based the GraalPy support on PyPy and added some small tests.
I'm open to discussing how to test this. GraalPy is available for
manylinux images and with setup-python, so we should be able to add
tests against it to the CI. I locally confirmed by installing `uv` into
a GraalPy venv and then trying things like `uv pip install Pillow` and
testing those extensions.

crates/uv-virtualenv/src/virtualenv.rs

@@ -178,6 +178,10 @@ pub(crate) fn create(
             )?;
             uv_fs::replace_symlink("python", scripts.join("pypy"))?;
         }
+
+        if interpreter.markers().implementation_name() == "graalpy" {
+            uv_fs::replace_symlink("python", scripts.join("graalpy"))?;
+        }
     }
 
     // No symlinking on Windows, at least not on a regular non-dev non-admin Windows install.
@@ -189,13 +193,31 @@ pub(crate) fn create(
             &scripts,
             python_home,
         )?;
-        copy_launcher_windows(
-            WindowsExecutable::Pythonw,
-            interpreter,
-            &base_python,
-            &scripts,
-            python_home,
-        )?;
+
+        if interpreter.markers().implementation_name() == "graalpy" {
+            copy_launcher_windows(
+                WindowsExecutable::GraalPy,
+                interpreter,
+                &base_python,
+                &scripts,
+                python_home,
+            )?;
+            copy_launcher_windows(
+                WindowsExecutable::PythonMajor,
+                interpreter,
+                &base_python,
+                &scripts,
+                python_home,
+            )?;
+        } else {
+            copy_launcher_windows(
+                WindowsExecutable::Pythonw,
+                interpreter,
+                &base_python,
+                &scripts,
+                python_home,
+            )?;
+        }
 
         if interpreter.markers().implementation_name() == "pypy" {
             copy_launcher_windows(
@@ -319,6 +341,16 @@ pub(crate) fn create(
         pyvenv_cfg_data.push(("prompt".to_string(), prompt));
     }
 
+    if cfg!(windows) && interpreter.markers().implementation_name() == "graalpy" {
+        pyvenv_cfg_data.push((
+            "venvlauncher_command".to_string(),
+            python_home
+                .join("graalpy.exe")
+                .simplified_display()
+                .to_string(),
+        ));
+    }
+
     let mut pyvenv_cfg = BufWriter::new(File::create(location.join("pyvenv.cfg"))?);
     write_cfg(&mut pyvenv_cfg, &pyvenv_cfg_data)?;
     drop(pyvenv_cfg);
@@ -380,6 +412,8 @@ enum WindowsExecutable {
     PyPyw,
     /// The `pypy3.<minor>w.exe` executable.
     PyPyMajorMinorw,
+    // The `graalpy.exe` executable
+    GraalPy,
 }
 
 impl WindowsExecutable {
@@ -417,6 +451,7 @@ impl WindowsExecutable {
                     interpreter.python_minor()
                 )
             }
+            WindowsExecutable::GraalPy => String::from("graalpy.exe"),
         }
     }
 
@@ -434,6 +469,7 @@ impl WindowsExecutable {
             WindowsExecutable::PyPyMajorMinor => "venvlauncher.exe",
             WindowsExecutable::PyPyw => "venvwlauncher.exe",
             WindowsExecutable::PyPyMajorMinorw => "venvwlauncher.exe",
+            WindowsExecutable::GraalPy => "venvlauncher.exe",
         }
     }
 }