Add basic PyEnv and pixi support for python environments (#37156)

cc https://github.com/zed-industries/zed/issues/29807

Release Notes:

- Fixed terminals and tasks not respecting python pyenv and pixi
environments

crates/language/src/toolchain.rs

@@ -14,6 +14,7 @@ use collections::HashMap;
 use fs::Fs;
 use gpui::{AsyncApp, SharedString};
 use settings::WorktreeId;
+use task::ShellKind;
 
 use crate::{LanguageName, ManifestName};
 
@@ -68,7 +69,12 @@ pub trait ToolchainLister: Send + Sync {
     fn term(&self) -> SharedString;
     /// Returns the name of the manifest file for this toolchain.
     fn manifest_name(&self) -> ManifestName;
-    async fn activation_script(&self, toolchain: &Toolchain, fs: &dyn Fs) -> Option<String>;
+    async fn activation_script(
+        &self,
+        toolchain: &Toolchain,
+        shell: ShellKind,
+        fs: &dyn Fs,
+    ) -> Vec<String>;
 }
 
 #[async_trait(?Send)]