Inject venv environment via the toolchain (#36576)

Instead of manually constructing the venv we now ask the python
toolchain for the relevant information, unifying the approach of vent
inspection

Fixes https://github.com/zed-industries/zed/issues/27350

Release Notes:

- Improved the detection of python virtual environments for terminals
and tasks in remote projects.

crates/project/src/project_tests.rs

@@ -9222,6 +9222,9 @@ fn python_lang(fs: Arc<FakeFs>) -> Arc<Language> {
         fn manifest_name(&self) -> ManifestName {
             SharedString::new_static("pyproject.toml").into()
         }
+        async fn activation_script(&self, _: &Toolchain, _: &dyn Fs) -> Option<String> {
+            None
+        }
     }
     Arc::new(
         Language::new(